{"id":112625,"date":"2026-10-04T09:25:10","date_gmt":"2026-10-04T01:25:10","guid":{"rendered":"https:\/\/www.wsisp.com\/helps\/112625.html"},"modified":"2026-10-04T09:25:10","modified_gmt":"2026-10-04T01:25:10","slug":"map-set-%e5%ae%8c%e5%85%a8%e6%8c%87%e5%8d%97%ef%bc%9a%e7%ba%a2%e9%bb%91%e6%a0%91%e4%b8%8e%e6%9c%89%e5%ba%8f%e5%ae%b9%e5%99%a8","status":"publish","type":"post","link":"https:\/\/www.wsisp.com\/helps\/112625.html","title":{"rendered":"map \/ set \u5b8c\u5168\u6307\u5357\uff1a\u7ea2\u9ed1\u6811\u4e0e\u6709\u5e8f\u5bb9\u5668"},"content":{"rendered":"

std::map \u662f C++ \u91cc\u6700\u5e38\u88ab\u7528\u3001\u4e5f\u6700\u5bb9\u6613\u88ab\u7528\u9519\u7684\u5bb9\u5668\u3002\u5b83\u7684\u6838\u5fc3\u4e8b\u5b9e\u53ea\u6709\u4e00\u53e5\u8bdd：\u5b83\u662f\u4e00\u68f5\u81ea\u5e73\u8861\u7684\u7ea2\u9ed1\u6811（red-black tree），\u6240\u4ee5 key \u6c38\u8fdc\u6709\u5e8f\u3001\u67e5\u627e\u6c38\u8fdc\u662f O(log n)\u3002\u6709\u5e8f\u5e26\u6765\u8303\u56f4\u67e5\u8be2\u3001\u4e2d\u5e8f\u904d\u5386\u5373\u6392\u5e8f\u3001find \u4f18\u4e8e std::find \u8fd9\u4e9b\u80fd\u529b；\u4f46\u4e5f\u5e26\u6765\u4e00\u4e2a\u8457\u540d\u9677\u9631\u2014\u2014operator[] \u5728\u627e\u4e0d\u5230 key \u65f6\u4f1a\u9ed8\u9ed8\u63d2\u5165\u4e00\u4e2a\u9ed8\u8ba4\u503c\u3002\u8fd9\u7bc7\u6309\u300c\u7ed3\u6784 \u2192 \u53ea\u8bfb\u67e5\u8868 \u2192 \u67e5\u627e\u5199\u6cd5 \u2192 \u63d2\u5165\u5199\u6cd5 \u2192 \u8303\u56f4\u67e5\u8be2 \u2192 \u5b8c\u6574\u793a\u4f8b\u300d\u7684\u987a\u5e8f\u628a map \/ set \u5168\u5bb6\u8bb2\u6e05\u695a\u3002<\/p>\n

1. \u5f15\u5b50：\u67e5\u4e00\u4e2a\u4e0d\u5b58\u5728\u7684 key，\u5bb9\u5668\u5374\u53d8\u5927\u4e86<\/h3>\n

\u5148\u770b\u4e00\u6bb5\u771f\u5b9e\u4ee3\u7801\u7684\u5b9e\u6d4b\u7ed3\u679c：<\/p>\n

size before = 1
\ninventory["banana"] = 0 but size becomes 2<\/p>\n

\u53ea\u662f\u300c\u8bfb\u4e00\u4e0b\u300dbanana \u7684\u6570\u91cf，\u5bb9\u5668\u7684 size \u5c31\u4ece 1 \u53d8\u6210\u4e86 2\u3002std::map::operator[] \u7684\u8bed\u4e49\u4e0d\u662f\u300c\u67e5\u300d，\u800c\u662f\u300c\u53d6\u5f15\u7528，\u4e0d\u5b58\u5728\u5c31\u63d2\u5165\u4e00\u4e2a\u503c\u521d\u59cb\u5316\u7684\u5143\u7d20\u300d\u3002\u4e00\u4e2a\u5e38\u89c1\u7684 bug \u662f\u62ff\u5b83\u5f53\u5224\u65ad：if (m[key] == 0) { … }\u2014\u2014\u6bcf\u6b21\u5224\u65ad\u90fd\u5728\u5f80 map \u91cc\u585e\u5783\u573e\u3002\u8981\u7406\u89e3\u4e3a\u4ec0\u4e48\u4f1a\u8fd9\u6837，\u5f97\u5148\u77e5\u9053 map \u5e95\u4e0b\u662f\u4ec0\u4e48\u3002<\/p>\n

2. \u7ea2\u9ed1\u6811：\u6709\u5e8f\u548c O(log n) \u662f\u540c\u4e00\u4e2a\u6765\u6e90<\/h3>\n

std::map<Key, T> \u4e0d\u662f\u54c8\u5e0c\u8868，\u4e5f\u4e0d\u662f\u666e\u901a\u4e8c\u53c9\u6811，\u800c\u662f\u7ea2\u9ed1\u6811\u2014\u2014\u4e00\u79cd\u6bcf\u4e2a\u8282\u70b9\u591a\u5e26\u4e00\u4f4d\u989c\u8272\u7684\u81ea\u5e73\u8861\u4e8c\u53c9\u641c\u7d22\u6811（binary search tree）\u3002<\/p>\n

\u7ea2\u9ed1\u6811（red-black tree）：\u4e00\u68f5\u81ea\u5e73\u8861\u7684\u4e8c\u53c9\u641c\u7d22\u6811，\u6bcf\u4e2a\u8282\u70b9\u591a\u4e00\u4f4d\u989c\u8272<\/p>\n

\u250c\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2510
\n \u2502 \u9ed1 50 \u2502 \u6839\u6c38\u8fdc\u662f\u9ed1
\n \u2514\u2500\u2500\u252c\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u252c\u2500\u2500\u2518
\n \u250c\u2500\u2500\u2500\u2500\u2500\u2500\u2518 \u2514\u2500\u2500\u2500\u2500\u2500\u2500\u2510
\n \u250c\u2500\u2500\u2500\u2500\u2500\u2500\u2534\u2500\u2500\u2500\u2500\u2500\u2500\u2510 \u250c\u2500\u2500\u2500\u2500\u2500\u2500\u2534\u2500\u2500\u2500\u2500\u2500\u2500\u2510
\n \u2502 \u7ea2 30 \u2502 \u2502 \u9ed1 70 \u2502
\n \u2514\u2500\u2500\u252c\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u252c\u2500\u2500\u2518 \u2514\u2500\u2500\u252c\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u252c\u2500\u2500\u2518
\n \u250c\u2500\u2500\u2500\u2500\u2518 \u2514\u2500\u2500\u2500\u2500\u2510 \u250c\u2500\u2500\u2500\u2500\u2500\u2518 \u2514\u2500\u2500\u2500\u2500\u2500\u2510
\n \u250c\u2500\u2500\u2500\u2500\u2534\u2500\u2500\u2500\u2510 \u250c\u2500\u2500\u2500\u2500\u2500\u2534\u2500\u2500\u2510 \u2502 … \u2502 …
\n \u2502 \u9ed1 20 \u2502 \u2502 \u9ed1 40 \u2502
\n \u2514\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2518 \u2514\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2518<\/p>\n

\u4e94\u6761\u7ea6\u675f（\u6559\u79d1\u4e66\u7248\u672c）：
\n \u2460 \u8282\u70b9\u975e\u7ea2\u5373\u9ed1 \u2461 \u6839\u662f\u9ed1
\n \u2462 \u53f6\u5b50（NIL \u7a7a\u8282\u70b9）\u90fd\u662f\u9ed1 \u2463 \u7ea2\u8282\u70b9\u7684\u5b69\u5b50\u5fc5\u987b\u662f\u9ed1（\u4e0d\u80fd\u8fde\u7eed\u4e24\u4e2a\u7ea2）
\n \u2464 \u4ece\u4efb\u4e00\u8282\u70b9\u5230\u5b83\u6240\u6709\u540e\u4ee3 NIL \u7684\u8def\u5f84\u4e0a，\u9ed1\u8282\u70b9\u4e2a\u6570\u76f8\u540c（\u9ed1\u9ad8\u76f8\u7b49）<\/p>\n

\u7531 \u2463\u2464 \u63a8\u51fa：\u6700\u957f\u8def\u5f84 <= 2 x \u6700\u77ed\u8def\u5f84 => \u6811\u9ad8 O(log n)\u3002
\n\u6240\u4ee5\u67e5\u627e\u3001\u63d2\u5165\u3001\u5220\u9664\u90fd\u662f O(log n)，\u800c\u4e14\u662f\u300c\u4fdd\u8bc1\u7684\u300d\u4e0a\u754c，
\n\u4e0d\u662f\u5e73\u5747\u60c5\u51b5 \u2014\u2014 \u8fd9\u4e00\u70b9\u548c\u4e0b\u9762\u8981\u8bb2\u7684 unordered_map \u6b63\u597d\u76f8\u53cd\u3002<\/p>\n

\u63d2\u5165\/\u5220\u9664\u7834\u574f\u4e86 \u2460\u2461\u2463\u2464 \u65f6，\u7528\u300c\u65cb\u8f6c（rotation）+ \u91cd\u65b0\u7740\u8272（recolor）\u300d
\n\u4fee\u56de\u6765，\u6bcf\u6b21\u53ea\u9700\u5e38\u6570\u6b21\u8c03\u6574，\u4ee3\u4ef7\u5df2\u7ecf\u7b97\u5728 O(log n) \u91cc\u3002<\/p>\n

\u4e2d\u5e8f\u904d\u5386\u8fd9\u68f5\u6811\u53d6\u51fa\u7684\u662f：20 30 40 50 70 …
\n\u2014\u2014 \u5929\u7136\u6709\u5e8f\u3002\u8fd9\u5c31\u662f map\/set \u80fd\u63d0\u4f9b lower_bound\/upper_bound \u7684\u539f\u56e0\u3002<\/p>\n

\u6ce8\u610f\u6700\u540e\u4e00\u884c：\u300c\u6709\u5e8f\u300d\u4e0d\u662f map \u989d\u5916\u7ef4\u62a4\u7684\u4e00\u4e2a\u5c5e\u6027，\u800c\u662f\u6811\u7ed3\u6784\u7684\u526f\u4ea7\u54c1\u3002\u4f60\u63d2\u5165 30\u300150\u300120\u300170\u300140，\u4e2d\u5e8f\u904d\u5386\u6c38\u8fdc\u662f 20 30 40 50 70，\u548c\u63d2\u5165\u987a\u5e8f\u65e0\u5173\u3002\u7ea2\u9ed1\u6811\u7684\u5177\u4f53\u5b9e\u73b0\u548c\u65cb\u8f6c\u7ec6\u8282\u4e0d\u5fc5\u80cc，\u8bb0\u4f4f\u4e24\u6761\u5c31\u591f\u7528：key \u6709\u5e8f\u3001\u6811\u9ad8\u88ab\u4fdd\u8bc1\u5728 O(log n)\u3002<\/p>\n

map \u5bb6\u65cf\u6709\u56db\u4e2a\u6210\u5458，\u533a\u522b\u53ea\u5728\u300c\u5141\u4e0d\u5141\u8bb8\u91cd\u590d\u300d：<\/p>\n\n\u5bb9\u5668\u91cd\u590d\u5143\u7d20\u6709\u5e8f\u6027\u67e5\u627e\u5178\u578b\u7528\u9014<\/tr>\n\n\n\n\n\n
std::map<K, V><\/td>\n\u4e0d\u5141\u8bb8\u91cd\u590d key<\/td>\n\u6309 key \u5347\u5e8f（\u53ef\u7528\u6bd4\u8f83\u5668\u6539）<\/td>\nO(log n)<\/td>\n\u952e\u503c\u6620\u5c04\u3001\u9700\u8981\u6709\u5e8f\u904d\u5386\u6216\u8303\u56f4\u67e5\u8be2<\/td>\n<\/tr>\n
std::set<K><\/td>\n\u4e0d\u5141\u8bb8\u91cd\u590d<\/td>\n\u5347\u5e8f<\/td>\nO(log n)<\/td>\n\u53bb\u91cd + \u6709\u5e8f\u904d\u5386<\/td>\n<\/tr>\n
std::multimap<K, V><\/td>\n\u5141\u8bb8\u91cd\u590d key<\/td>\n\u6709\u5e8f<\/td>\nO(log n)<\/td>\n\u4e00\u5bf9\u591a（\u5206\u6570\u2192\u59d3\u540d\u3001\u7d22\u5f15\u5012\u6392）<\/td>\n<\/tr>\n
std::multiset<K><\/td>\n\u5141\u8bb8\u91cd\u590d<\/td>\n\u6709\u5e8f<\/td>\nO(log n)<\/td>\n\u6709\u5e8f\u888b\u3001\u6ed1\u52a8\u7a97\u53e3\u4e2d\u4f4d\u6570<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

\/\/ map_basic.cpp \u2014 \u7f16\u8bd1: g++ -std=c++17 -Wall -O2 map_basic.cpp -o map_basic<\/span>
\n#<\/span>include<\/span> <iostream><\/span><\/span>
\n#<\/span>include<\/span> <map><\/span><\/span>
\n#<\/span>include<\/span> <set><\/span><\/span>
\n#<\/span>include<\/span> <string><\/span><\/span><\/p>\n

int<\/span> main<\/span>(<\/span>)<\/span> {<\/span>
\n std::<\/span>map<<\/span>std::<\/span>string,<\/span> int<\/span>><\/span> ages;<\/span>
\n ages[<\/span>"alice"<\/span>]<\/span> =<\/span> 30<\/span>;<\/span>
\n ages[<\/span>"bob"<\/span>]<\/span> =<\/span> 25<\/span>;<\/span>
\n ages[<\/span>"carol"<\/span>]<\/span> =<\/span> 35<\/span>;<\/span><\/p>\n

std::<\/span>cout <<<\/span> "map iteration (sorted by key):"<\/span>;<\/span>
\n for<\/span> (<\/span>const<\/span> auto<\/span>&<\/span> [<\/span>name,<\/span> age]<\/span> :<\/span> ages)<\/span> std::<\/span>cout <<<\/span> ' '<\/span> <<<\/span> name <<<\/span> '='<\/span> <<<\/span> age;<\/span>
\n std::<\/span>cout <<<\/span> '\\\\n'<\/span>;<\/span><\/p>\n

\/\/ insert \u8fd4\u56de pair<iterator, bool>：bool \u8bf4\u660e\u5230\u5e95\u63d2\u8fdb\u53bb\u4e86\u6ca1\u6709<\/span>
\n const<\/span> auto<\/span> [<\/span>it1,<\/span> inserted1]<\/span> =<\/span> ages.<\/span>insert<\/span>(<\/span>{<\/span>"dave"<\/span>,<\/span> 40<\/span>}<\/span>)<\/span>;<\/span>
\n const<\/span> auto<\/span> [<\/span>it2,<\/span> inserted2]<\/span> =<\/span> ages.<\/span>insert<\/span>(<\/span>{<\/span>"bob"<\/span>,<\/span> 99<\/span>}<\/span>)<\/span>;<\/span>
\n std::<\/span>cout <<<\/span> "insert dave: inserted="<\/span> <<<\/span> inserted1 <<<\/span> " value="<\/span> <<<\/span> it1-><\/span>second <<<\/span> '\\\\n'<\/span>;<\/span>
\n std::<\/span>cout <<<\/span> "insert bob : inserted="<\/span> <<<\/span> inserted2 <<<\/span> " value="<\/span> <<<\/span> it2-><\/span>second <<<\/span> '\\\\n'<\/span>;<\/span><\/p>\n

std::<\/span>set<<\/span>int<\/span>><\/span> uniq{<\/span>3<\/span>,<\/span> 1<\/span>,<\/span> 4<\/span>,<\/span> 1<\/span>,<\/span> 5<\/span>,<\/span> 9<\/span>,<\/span> 2<\/span>,<\/span> 6<\/span>}<\/span>;<\/span>
\n std::<\/span>cout <<<\/span> "set (dedup + sorted):"<\/span>;<\/span>
\n for<\/span> (<\/span>int<\/span> v :<\/span> uniq)<\/span> std::<\/span>cout <<<\/span> ' '<\/span> <<<\/span> v;<\/span>
\n std::<\/span>cout <<<\/span> "\\\\nset size = "<\/span> <<<\/span> uniq.<\/span>size<\/span>(<\/span>)<\/span> <<<\/span> '\\\\n'<\/span>;<\/span>
\n std::<\/span>cout <<<\/span> "count(4) = "<\/span> <<<\/span> uniq.<\/span>count<\/span>(<\/span>4<\/span>)<\/span> <<<\/span> " count(7) = "<\/span> <<<\/span> uniq.<\/span>count<\/span>(<\/span>7<\/span>)<\/span> <<<\/span> '\\\\n'<\/span>;<\/span>
\n return<\/span> 0<\/span>;<\/span>
\n}<\/span><\/p>\n

map iteration (sorted by key): alice=30 bob=25 carol=35
\ninsert dave: inserted=1 value=40
\ninsert bob : inserted=0 value=25
\nset (dedup + sorted): 1 2 3 4 5 6 9
\nset size = 7
\ncount(4) = 1 count(7) = 0<\/p>\n

\u4e09\u5904\u7ec6\u8282\u90fd\u503c\u5f97\u8bb0\u4f4f：\u904d\u5386\u8f93\u51fa\u662f alice bob carol \u800c\u4e0d\u662f\u63d2\u5165\u987a\u5e8f（\u7ea2\u9ed1\u6811\u7684\u4e2d\u5e8f\u5373\u5b57\u5178\u5e8f）；insert("bob", 99) \u8fd4\u56de inserted=0, value=25\u2014\u2014\u6ca1\u6709\u8986\u76d6，\u539f\u6765\u7684 25 \u8fd8\u5728，\u8fd9\u662f insert \u4e0e operator[] \u6700\u672c\u8d28\u7684\u533a\u522b；set \u628a\u91cd\u590d\u51fa\u73b0\u7684 1 \u53bb\u6389\u4e86\u5e76\u6392\u597d\u5e8f，count \u5c31\u662f\u300c\u5728\u4e0d\u5728\u300d\u7684\u5224\u636e\u3002<\/p>\n

\u5b98\u65b9\u6587\u6863：std::map \u2014 cppreference \u5b98\u65b9\u6587\u6863：std::set \u2014 cppreference \u5b98\u65b9\u6587\u6863：std::multimap \u2014 cppreference<\/p>\n

3. \u9677\u9631\u4e00：operator[] \u627e\u4e0d\u5230\u5c31\u63d2\u5165<\/h3>\n

operator[] \u7684\u5b8c\u6574\u8bed\u4e49\u662f\u300c\u8fd4\u56de key \u5bf9\u5e94 value \u7684\u5f15\u7528；key \u4e0d\u5b58\u5728\u5c31\u5148\u7528\u9ed8\u8ba4\u6784\u9020\u585e\u4e00\u4e2a\u8fdb\u53bb，\u518d\u8fd4\u56de\u5b83\u7684\u5f15\u7528\u300d\u3002\u6240\u4ee5\u5b83\u6709\u4e09\u4e2a\u540e\u679c：\u5bb9\u5668\u4f1a\u88ab\u6539（size \u53d8\u5927）；value \u7c7b\u578b\u5fc5\u987b\u53ef\u9ed8\u8ba4\u6784\u9020（\u5426\u5219\u7f16\u8bd1\u4e0d\u8fc7）；const map \u4e0a\u6839\u672c\u4e0d\u80fd\u7528\u5b83\u3002<\/p>\n

operator[] \u5728\u5199\u5165\u573a\u666f\u5f88\u597d\u7528（histogram[word]++ \u662f\u6807\u51c6\u5199\u6cd5），\u4f46\u53ea\u8bfb\u573a\u666f\u5fc5\u987b\u6362 API：<\/p>\n

\/\/ map_subscript.cpp \u2014 \u7f16\u8bd1: g++ -std=c++17 -Wall -O2 map_subscript.cpp -o map_subscript<\/span>
\n#<\/span>include<\/span> <iostream><\/span><\/span>
\n#<\/span>include<\/span> <map><\/span><\/span>
\n#<\/span>include<\/span> <stdexcept><\/span><\/span>
\n#<\/span>include<\/span> <string><\/span><\/span><\/p>\n

int<\/span> main<\/span>(<\/span>)<\/span> {<\/span>
\n std::<\/span>map<<\/span>std::<\/span>string,<\/span> int<\/span>><\/span> inventory{<\/span>{<\/span>"apple"<\/span>,<\/span> 3<\/span>}<\/span>}<\/span>;<\/span>
\n std::<\/span>cout <<<\/span> "size before = "<\/span> <<<\/span> inventory.<\/span>size<\/span>(<\/span>)<\/span> <<<\/span> '\\\\n'<\/span>;<\/span><\/p>\n

const<\/span> int<\/span> missing =<\/span> inventory[<\/span>"banana"<\/span>]<\/span>;<\/span> \/\/ \u53cd\u4f8b，\u4e0d\u8981\u8fd9\u4e48\u5199：\u8bfb\u4e00\u4e0b\u5c31\u63d2\u8fdb\u53bb\u4e86<\/span>
\n std::<\/span>cout <<<\/span> "inventory[\\\\"banana\\\\"] = "<\/span> <<<\/span> missing
\n <<<\/span> " but size becomes "<\/span> <<<\/span> inventory.<\/span>size<\/span>(<\/span>)<\/span> <<<\/span> '\\\\n'<\/span>;<\/span><\/p>\n

const<\/span> auto<\/span> found =<\/span> inventory.<\/span>find<\/span>(<\/span>"cherry"<\/span>)<\/span>;<\/span> \/\/ \u53ea\u8bfb\u67e5\u8be2：\u627e\u4e0d\u5230\u4e0d\u4f1a\u6539\u5bb9\u5668<\/span>
\n std::<\/span>cout <<<\/span> "find(\\\\"cherry\\\\") == end() ? "<\/span> <<<\/span> (<\/span>found ==<\/span> inventory.<\/span>end<\/span>(<\/span>)<\/span>)<\/span>
\n <<<\/span> " size = "<\/span> <<<\/span> inventory.<\/span>size<\/span>(<\/span>)<\/span> <<<\/span> '\\\\n'<\/span>;<\/span><\/p>\n

try<\/span> {<\/span>
\n std::<\/span>cout <<<\/span> inventory.<\/span>at<\/span>(<\/span>"cherry"<\/span>)<\/span> <<<\/span> '\\\\n'<\/span>;<\/span>
\n }<\/span> catch<\/span> (<\/span>const<\/span> std::<\/span>out_of_range&<\/span> e)<\/span> {<\/span> \/\/ \u5f02\u5e38\u6309\u5f15\u7528\u6355，\u6309\u503c\u629b<\/span>
\n std::<\/span>cout <<<\/span> "at(\\\\"cherry\\\\") threw std::out_of_range: "<\/span> <<<\/span> e.<\/span>what<\/span>(<\/span>)<\/span> <<<\/span> '\\\\n'<\/span>;<\/span>
\n }<\/span><\/p>\n

const<\/span> std::<\/span>map<<\/span>std::<\/span>string,<\/span> int<\/span>><\/span>&<\/span> frozen =<\/span> inventory;<\/span>
\n std::<\/span>cout <<<\/span> "size still = "<\/span> <<<\/span> frozen.<\/span>size<\/span>(<\/span>)<\/span> <<<\/span> '\\\\n'<\/span>;<\/span>
\n return<\/span> 0<\/span>;<\/span>
\n}<\/span><\/p>\n

size before = 1
\ninventory["banana"] = 0 but size becomes 2
\nfind("cherry") == end() ? 1 size = 2
\nat("cherry") threw std::out_of_range: map::at
\nsize still = 2<\/p>\n

\u4e09\u79cd\u53ea\u8bfb\u5199\u6cd5\u5404\u6709\u53d6\u820d：<\/p>\n\n\u5199\u6cd5\u627e\u4e0d\u5230\u65f6\u80fd\u7528\u5728 const map \u4e0a\u590d\u6742\u5ea6\u4ec0\u4e48\u65f6\u5019\u7528<\/tr>\n\n\n\n\n\n\n
m[key]<\/td>\n\u63d2\u5165\u9ed8\u8ba4\u503c（size +1）<\/td>\n\u4e0d\u80fd<\/td>\nO(log n)<\/td>\n\u53ea\u5728\u300c\u5199\u300d\u7684\u8bed\u4e49\u4e0b\u7528，\u5982 m[k]++<\/td>\n<\/tr>\n
m.at(key)<\/td>\n\u629b std::out_of_range<\/td>\n\u80fd<\/td>\nO(log n)<\/td>\n\u903b\u8f91\u4e0a\u5fc5\u987b\u5b58\u5728，\u4e0d\u5b58\u5728\u5c31\u662f bug<\/td>\n<\/tr>\n
m.find(key)<\/td>\n\u8fd4\u56de end()<\/td>\n\u80fd<\/td>\nO(log n)<\/td>\n\u5e38\u89c4\u53ea\u8bfb\u67e5\u8be2，\u8fd8\u8981\u62ff value<\/td>\n<\/tr>\n
m.count(key)<\/td>\n\u8fd4\u56de 0<\/td>\n\u80fd<\/td>\nO(log n)<\/td>\n\u53ea\u5224\u65ad\u5b58\u5728\u6027<\/td>\n<\/tr>\n
m.contains(key)<\/td>\n\u8fd4\u56de false<\/td>\n\u80fd<\/td>\nO(log n)<\/td>\nC++20 \u8d77\u53ef\u7528，\u8bed\u4e49\u6700\u76f4\u767d<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

at \u629b\u51fa\u7684\u5f02\u5e38\u4fe1\u606f\u91cc\u90a3\u53e5 map::at \u662f libstdc++ \u7684\u5b9e\u73b0\u7ec6\u8282（\u6807\u51c6\u53ea\u8981\u6c42\u629b std::out_of_range，\u6ca1\u89c4\u5b9a what() \u5185\u5bb9），\u6362\u7f16\u8bd1\u5668\u53ef\u80fd\u4e0d\u540c，\u4e0d\u8981\u62ff\u53bb\u5339\u914d\u5b57\u7b26\u4e32\u3002<\/p>\n

\u5b98\u65b9\u6587\u6863：std::map::operator[] \u2014 cppreference：\u5b98\u65b9\u7b2c\u4e00\u53e5\u8bdd\u5c31\u5199\u7740\u300c\u82e5 key \u4e0d\u5b58\u5728\u5219\u63d2\u5165 value_type(key, T())\u300d\u3002 \u5b98\u65b9\u6587\u6863：std::map::at \u2014 cppreference \u5b98\u65b9\u6587\u6863：std::map::contains（C++20）\u2014 cppreference<\/p>\n

C++20 \u624d\u6709 contains，\u5728 C++17 \u91cc\u7528 count \u4ee3\u66ff：<\/p>\n

\/\/ verify: std=c++20<\/span>
\n#<\/span>include<\/span> <map><\/span><\/span><\/p>\n

bool<\/span> has_key<\/span>(<\/span>const<\/span> std::<\/span>map<<\/span>int<\/span>,<\/span> int<\/span>><\/span>&<\/span> table,<\/span> int<\/span> key)<\/span> {<\/span>
\n return<\/span> table.<\/span>contains<\/span>(<\/span>key)<\/span>;<\/span> \/\/ \u9700\u8981 C++20；C++17 \u5199 table.count(key) != 0<\/span>
\n}<\/span><\/p>\n

4. \u9677\u9631\u4e8c：\u62ff std::find \u53bb\u67e5 map<\/h3>\n

\u300cmap \u7684\u67e5\u627e\u5feb\u300d\u4e0d\u662f\u4fee\u8f9e\u3002std::map::find \u8d70\u7684\u662f\u7ea2\u9ed1\u6811\u7684\u641c\u7d22\u8def\u5f84，\u4e00\u6b21\u6bd4\u8f83\u5c31\u628a\u5019\u9009\u8303\u56f4\u780d\u4e00\u534a；\u800c std::find \/ std::find_if \u662f\u4ece begin() \u5f00\u59cb\u9010\u4e2a\u7ebf\u6027\u626b\u63cf，\u5b8c\u5168\u65e0\u89c6\u6811\u7ed3\u6784\u3002\u7ed9 map \u7684 key \u88c5\u4e00\u4e2a\u8ba1\u6570\u6bd4\u8f83\u5668\u3001\u518d\u7ed9 find_if \u7684\u8c13\u8bcd\u88c5\u4e00\u4e2a\u8ba1\u6570\u5668，\u5c31\u80fd\u91cf\u51fa\u5dee\u8ddd：<\/p>\n

\/\/ map_find_vs_std_find.cpp \u2014 \u7f16\u8bd1: g++ -std=c++17 -Wall -O2 map_find_vs_std_find.cpp -o map_find_vs_std_find<\/span>
\n#<\/span>include<\/span> <algorithm><\/span><\/span>
\n#<\/span>include<\/span> <cstddef><\/span><\/span>
\n#<\/span>include<\/span> <iostream><\/span><\/span>
\n#<\/span>include<\/span> <map><\/span><\/span><\/p>\n

struct<\/span> Stats<\/span> {<\/span>
\n inline<\/span> static<\/span> std::<\/span>size_t comparisons =<\/span> 0<\/span>;<\/span> \/\/ map \u5185\u90e8\u6bd4\u8f83\u6b21\u6570<\/span>
\n inline<\/span> static<\/span> std::<\/span>size_t predicate_calls =<\/span> 0<\/span>;<\/span> \/\/ find_if \u8c13\u8bcd\u8c03\u7528\u6b21\u6570<\/span>
\n}<\/span>;<\/span><\/p>\n

struct<\/span> Key<\/span> {<\/span>
\n int<\/span> id =<\/span> 0<\/span>;<\/span>
\n}<\/span>;<\/span><\/p>\n

struct<\/span> CountingLess<\/span> {<\/span>
\n bool<\/span> operator<\/span>(<\/span>)<\/span>(<\/span>const<\/span> Key&<\/span> a,<\/span> const<\/span> Key&<\/span> b)<\/span> const<\/span> {<\/span>
\n ++<\/span>Stats::<\/span>comparisons;<\/span>
\n return<\/span> a.<\/span>id <<\/span> b.<\/span>id;<\/span>
\n }<\/span>
\n}<\/span>;<\/span><\/p>\n

constexpr<\/span> int<\/span> N =<\/span> 1000<\/span>;<\/span><\/p>\n

int<\/span> main<\/span>(<\/span>)<\/span> {<\/span>
\n std::<\/span>map<<\/span>Key,<\/span> int<\/span>,<\/span> CountingLess><\/span> table;<\/span>
\n for<\/span> (<\/span>int<\/span> i =<\/span> 0<\/span>;<\/span> i <<\/span> N;<\/span> ++<\/span>i)<\/span> table.<\/span>emplace<\/span>(<\/span>Key{<\/span>i}<\/span>,<\/span> i *<\/span> 10<\/span>)<\/span>;<\/span><\/p>\n

const<\/span> Key target{<\/span>500<\/span>}<\/span>;<\/span> \/\/ \u6b63\u597d\u5728\u4e2d\u95f4<\/span><\/p>\n

Stats::<\/span>comparisons =<\/span> 0<\/span>;<\/span>
\n const<\/span> auto<\/span> by_tree =<\/span> table.<\/span>find<\/span>(<\/span>target)<\/span>;<\/span>
\n const<\/span> std::<\/span>size_t tree_cmp =<\/span> Stats::<\/span>comparisons;<\/span><\/p>\n

Stats::<\/span>predicate_calls =<\/span> 0<\/span>;<\/span>
\n const<\/span> auto<\/span> by_scan =<\/span> std::<\/span>find_if<\/span>(<\/span>table.<\/span>begin<\/span>(<\/span>)<\/span>,<\/span> table.<\/span>end<\/span>(<\/span>)<\/span>,<\/span>
\n [<\/span>&<\/span>target]<\/span>(<\/span>const<\/span> auto<\/span>&<\/span> kv)<\/span> {<\/span>
\n ++<\/span>Stats::<\/span>predicate_calls;<\/span>
\n return<\/span> kv.<\/span>first.<\/span>id ==<\/span> target.<\/span>id;<\/span>
\n }<\/span>)<\/span>;<\/span><\/p>\n

std::<\/span>cout <<<\/span> "keys = "<\/span> <<<\/span> N <<<\/span> '\\\\n'<\/span>;<\/span>
\n std::<\/span>cout <<<\/span> "map::find comparisons = "<\/span> <<<\/span> tree_cmp
\n <<<\/span> " found="<\/span> <<<\/span> (<\/span>by_tree !=<\/span> table.<\/span>end<\/span>(<\/span>)<\/span>)<\/span> <<<\/span> '\\\\n'<\/span>;<\/span>
\n std::<\/span>cout <<<\/span> "std::find_if calls = "<\/span> <<<\/span> Stats::<\/span>predicate_calls
\n <<<\/span> " found="<\/span> <<<\/span> (<\/span>by_scan !=<\/span> table.<\/span>end<\/span>(<\/span>)<\/span>)<\/span> <<<\/span> '\\\\n'<\/span>;<\/span>
\n return<\/span> 0<\/span>;<\/span>
\n}<\/span><\/p>\n

keys = 1000
\nmap::find comparisons = 11 found=1
\nstd::find_if calls = 501 found=1<\/p>\n

\u540c\u6837\u662f\u300c\u67e5\u4e00\u4e2a\u5b58\u5728\u7684 key\u300d：<\/p>\n\n\u5199\u6cd5\u4f9d\u636e\u590d\u6742\u5ea61000 \u4e2a key \u7684\u5b9e\u6d4b<\/tr>\n\n\n\n
table.find(k)<\/td>\n\u7ea2\u9ed1\u6811\u641c\u7d22\u8def\u5f84，\u6bcf\u6b21\u6bd4\u8f83\u780d\u4e00\u534a<\/td>\nO(log n)<\/td>\n11 \u6b21\u6bd4\u8f83<\/td>\n<\/tr>\n
std::find_if(m.begin(), m.end(), …)<\/td>\n\u4ece\u5934\u90e8\u7ebf\u6027\u626b\u63cf<\/td>\nO(n)<\/td>\n501 \u6b21\u8c13\u8bcd\u8c03\u7528<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

11 \u6b21\u6bd4\u8f83\u6b63\u597d\u662f log\u2082(1000) \u2248 10 \u7684\u91cf\u7ea7（\u7ea2\u9ed1\u6811\u6700\u957f\u8def\u5f84\u4e0d\u8d85\u8fc7 2log\u2082(n+1)）；501 \u6b21\u662f\u300c\u76ee\u6807\u5728\u4e2d\u95f4\u300d\u7684\u5fc5\u7136\u7ed3\u679c\u3002\u89c4\u6a21\u518d\u5927\u5341\u500d，\u524d\u8005\u53ea\u591a 3～4 \u6b21，\u540e\u8005\u591a\u5341\u500d\u3002\u7528\u4e86 map \u5374\u62ff std::find \u53bb\u67e5，\u7b49\u4e8e\u628a O(log n) \u4eb2\u624b\u964d\u7ea7\u6210 O(n)\u3002<\/p>\n

\u5b98\u65b9\u6587\u6863：std::map::find \u2014 cppreference：\u6807\u6ce8\u7684\u590d\u6742\u5ea6\u5c31\u662f\u300c\u4e0e\u5bb9\u5668\u5927\u5c0f\u7684\u5bf9\u6570\u6210\u6b63\u6bd4\u300d\u3002 \u5b98\u65b9\u6587\u6863：std::find_if \u2014 cppreference：\u7ebf\u6027\u626b\u63cf\u7684\u6cdb\u578b\u7248\u672c\u3002<\/p>\n

5. \u63d2\u5165 API \u9009\u578b：\u4e94\u79cd\u5199\u6cd5，\u6784\u9020\u6b21\u6570\u5dee\u4e00\u500d<\/h3>\n

map \u4e00\u6b21\u6027\u63d0\u4f9b\u4e86\u4e94\u79cd\u300c\u63d2\u5165\u6216\u66f4\u65b0\u300d\u7684\u5199\u6cd5，\u5b83\u4eec\u7684\u533a\u522b\u5168\u5728\u6784\u9020\/\u62f7\u8d1d\/\u79fb\u52a8\u7684\u6b21\u6570\u4ee5\u53cakey \u5df2\u5b58\u5728\u65f6\u7684\u884c\u4e3a\u3002\u7528\u4e00\u4e2a\u81ea\u5e26\u8ba1\u6570\u5668\u7684 value \u7c7b\u578b\u5b9e\u6d4b\u4e00\u904d：<\/p>\n

\/\/ map_emplace.cpp \u2014 \u7f16\u8bd1: g++ -std=c++17 -Wall -O2 map_emplace.cpp -o map_emplace<\/span>
\n#<\/span>include<\/span> <cstddef><\/span><\/span>
\n#<\/span>include<\/span> <iostream><\/span><\/span>
\n#<\/span>include<\/span> <map><\/span><\/span>
\n#<\/span>include<\/span> <string><\/span><\/span><\/p>\n

struct<\/span> WidgetStats<\/span> {<\/span>
\n inline<\/span> static<\/span> std::<\/span>size_t default_ctors =<\/span> 0<\/span>;<\/span>
\n inline<\/span> static<\/span> std::<\/span>size_t value_ctors =<\/span> 0<\/span>;<\/span>
\n inline<\/span> static<\/span> std::<\/span>size_t copies =<\/span> 0<\/span>;<\/span>
\n inline<\/span> static<\/span> std::<\/span>size_t moves =<\/span> 0<\/span>;<\/span>
\n static<\/span> void<\/span> reset<\/span>(<\/span>)<\/span> {<\/span> default_ctors =<\/span> 0<\/span>;<\/span> value_ctors =<\/span> 0<\/span>;<\/span> copies =<\/span> 0<\/span>;<\/span> moves =<\/span> 0<\/span>;<\/span> }<\/span>
\n static<\/span> std::<\/span>size_t ctors<\/span>(<\/span>)<\/span> {<\/span> return<\/span> default_ctors +<\/span> value_ctors;<\/span> }<\/span>
\n}<\/span>;<\/span><\/p>\n

struct<\/span> Widget<\/span> {<\/span>
\n int<\/span> id =<\/span> 0<\/span>;<\/span><\/p>\n

Widget<\/span>(<\/span>)<\/span> {<\/span> ++<\/span>WidgetStats::<\/span>default_ctors;<\/span> }<\/span>
\n explicit<\/span> Widget<\/span>(<\/span>int<\/span> v)<\/span> :<\/span> id<\/span>(<\/span>v)<\/span> {<\/span> ++<\/span>WidgetStats::<\/span>value_ctors;<\/span> }<\/span>
\n Widget<\/span>(<\/span>const<\/span> Widget&<\/span> other)<\/span> :<\/span> id<\/span>(<\/span>other.<\/span>id)<\/span> {<\/span> ++<\/span>WidgetStats::<\/span>copies;<\/span> }<\/span>
\n Widget<\/span>(<\/span>Widget&&<\/span> other)<\/span> noexcept<\/span> :<\/span> id<\/span>(<\/span>other.<\/span>id)<\/span> {<\/span> ++<\/span>WidgetStats::<\/span>moves;<\/span> }<\/span>
\n Widget&<\/span> operator<\/span>=<\/span>(<\/span>const<\/span> Widget&<\/span> other)<\/span> {<\/span> id =<\/span> other.<\/span>id;<\/span> ++<\/span>WidgetStats::<\/span>copies;<\/span> return<\/span> *<\/span>this<\/span>;<\/span> }<\/span>
\n Widget&<\/span> operator<\/span>=<\/span>(<\/span>Widget&&<\/span> other)<\/span> noexcept<\/span> {<\/span> id =<\/span> other.<\/span>id;<\/span> ++<\/span>WidgetStats::<\/span>moves;<\/span> return<\/span> *<\/span>this<\/span>;<\/span> }<\/span>
\n}<\/span>;<\/span><\/p>\n

void<\/span> report<\/span>(<\/span>const<\/span> char<\/span>*<\/span> label)<\/span> {<\/span>
\n std::<\/span>cout <<<\/span> label <<<\/span> " ctors="<\/span> <<<\/span> WidgetStats<\/span>::<\/span>ctors<\/span>(<\/span>)<\/span>
\n <<<\/span> " copies="<\/span> <<<\/span> WidgetStats::<\/span>copies
\n <<<\/span> " moves="<\/span> <<<\/span> WidgetStats::<\/span>moves <<<\/span> '\\\\n'<\/span>;<\/span>
\n}<\/span><\/p>\n

int<\/span> main<\/span>(<\/span>)<\/span> {<\/span>
\n {<\/span>
\n std::<\/span>map<<\/span>std::<\/span>string,<\/span> Widget><\/span> m;<\/span>
\n WidgetStats<\/span>::<\/span>reset<\/span>(<\/span>)<\/span>;<\/span>
\n m[<\/span>"a"<\/span>]<\/span> =<\/span> Widget{<\/span>1<\/span>}<\/span>;<\/span> \/\/ \u9ed8\u8ba4\u6784\u9020\u4e00\u4e2a + \u79fb\u52a8\u8d4b\u503c<\/span>
\n report<\/span>(<\/span>"operator[] "<\/span>)<\/span>;<\/span>
\n }<\/span>
\n {<\/span>
\n std::<\/span>map<<\/span>std::<\/span>string,<\/span> Widget><\/span> m;<\/span>
\n WidgetStats<\/span>::<\/span>reset<\/span>(<\/span>)<\/span>;<\/span>
\n m.<\/span>insert<\/span>(<\/span>{<\/span>"b"<\/span>,<\/span> Widget{<\/span>2<\/span>}<\/span>}<\/span>)<\/span>;<\/span> \/\/ \u6784\u9020\u4e34\u65f6 pair \u518d\u79fb\u52a8\u8fdb\u8282\u70b9<\/span>
\n report<\/span>(<\/span>"insert "<\/span>)<\/span>;<\/span>
\n }<\/span>
\n {<\/span>
\n std::<\/span>map<<\/span>std::<\/span>string,<\/span> Widget><\/span> m;<\/span>
\n WidgetStats<\/span>::<\/span>reset<\/span>(<\/span>)<\/span>;<\/span>
\n m.<\/span>emplace<\/span>(<\/span>"c"<\/span>,<\/span> 3<\/span>)<\/span>;<\/span> \/\/ \u5c31\u5730\u5728\u8282\u70b9\u91cc\u6784\u9020，\u96f6\u4e34\u65f6\u5bf9\u8c61<\/span>
\n report<\/span>(<\/span>"emplace "<\/span>)<\/span>;<\/span>
\n }<\/span>
\n {<\/span>
\n std::<\/span>map<<\/span>std::<\/span>string,<\/span> Widget><\/span> m;<\/span>
\n WidgetStats<\/span>::<\/span>reset<\/span>(<\/span>)<\/span>;<\/span>
\n m.<\/span>try_emplace<\/span>(<\/span>"d"<\/span>,<\/span> 4<\/span>)<\/span>;<\/span> \/\/ key \u4e0d\u5b58\u5728\u624d\u6784\u9020（C++17）<\/span>
\n report<\/span>(<\/span>"try_emplace "<\/span>)<\/span>;<\/span>
\n }<\/span>
\n {<\/span>
\n std::<\/span>map<<\/span>std::<\/span>string,<\/span> Widget><\/span> m;<\/span>
\n m.<\/span>emplace<\/span>(<\/span>"e"<\/span>,<\/span> 5<\/span>)<\/span>;<\/span>
\n WidgetStats<\/span>::<\/span>reset<\/span>(<\/span>)<\/span>;<\/span>
\n m.<\/span>emplace<\/span>(<\/span>"e"<\/span>,<\/span> 9<\/span>)<\/span>;<\/span> \/\/ key \u5df2\u5b58\u5728：\u767d\u6784\u9020\u4e00\u4e2a\u518d\u4e22\u6389<\/span>
\n report<\/span>(<\/span>"emplace dup "<\/span>)<\/span>;<\/span>
\n std::<\/span>cout <<<\/span> " kept = "<\/span> <<<\/span> m.<\/span>at<\/span>(<\/span>"e"<\/span>)<\/span>.<\/span>id <<<\/span> '\\\\n'<\/span>;<\/span>
\n }<\/span>
\n {<\/span>
\n std::<\/span>map<<\/span>std::<\/span>string,<\/span> Widget><\/span> m;<\/span>
\n m.<\/span>emplace<\/span>(<\/span>"f"<\/span>,<\/span> 5<\/span>)<\/span>;<\/span>
\n WidgetStats<\/span>::<\/span>reset<\/span>(<\/span>)<\/span>;<\/span>
\n m.<\/span>try_emplace<\/span>(<\/span>"f"<\/span>,<\/span> 9<\/span>)<\/span>;<\/span> \/\/ key \u5df2\u5b58\u5728：\u4e00\u4e2a\u5bf9\u8c61\u90fd\u4e0d\u6784\u9020<\/span>
\n report<\/span>(<\/span>"try_emplace dup "<\/span>)<\/span>;<\/span>
\n std::<\/span>cout <<<\/span> " kept = "<\/span> <<<\/span> m.<\/span>at<\/span>(<\/span>"f"<\/span>)<\/span>.<\/span>id <<<\/span> '\\\\n'<\/span>;<\/span>
\n }<\/span>
\n {<\/span>
\n std::<\/span>map<<\/span>std::<\/span>string,<\/span> Widget><\/span> m;<\/span>
\n m.<\/span>emplace<\/span>(<\/span>"g"<\/span>,<\/span> 5<\/span>)<\/span>;<\/span>
\n WidgetStats<\/span>::<\/span>reset<\/span>(<\/span>)<\/span>;<\/span>
\n m.<\/span>insert_or_assign<\/span>(<\/span>"g"<\/span>,<\/span> Widget{<\/span>9<\/span>}<\/span>)<\/span>;<\/span> \/\/ C++17：\u660e\u786e\u8981\u8986\u76d6<\/span>
\n report<\/span>(<\/span>"insert_or_assign"<\/span>)<\/span>;<\/span>
\n std::<\/span>cout <<<\/span> " kept = "<\/span> <<<\/span> m.<\/span>at<\/span>(<\/span>"g"<\/span>)<\/span>.<\/span>id <<<\/span> '\\\\n'<\/span>;<\/span>
\n }<\/span>
\n return<\/span> 0<\/span>;<\/span>
\n}<\/span><\/p>\n

operator[] ctors=2 copies=0 moves=1
\ninsert ctors=1 copies=0 moves=2
\nemplace ctors=1 copies=0 moves=0
\ntry_emplace ctors=1 copies=0 moves=0
\nemplace dup ctors=1 copies=0 moves=0
\n kept = 5
\ntry_emplace dup ctors=0 copies=0 moves=0
\n kept = 5
\ninsert_or_assign ctors=1 copies=0 moves=1
\n kept = 9<\/p>\n

\u628a\u8fd9\u4e9b\u6570\u5b57\u7ffb\u8bd1\u6210\u4eba\u8bdd：<\/p>\n\n\u5199\u6cd5key \u5df2\u5b58\u5728\u65f6\u6784\u9020\u6b21\u6570\u62f7\u8d1d\/\u79fb\u52a8\u5b9e\u6d4b（ctors\/copies\/moves）\u4ec0\u4e48\u65f6\u5019\u7528<\/tr>\n\n\n\n\n\n\n
m[k] = v<\/td>\n\u8986\u76d6<\/td>\n2（\u9ed8\u8ba4\u6784\u9020 + \u8d4b\u503c）<\/td>\n1 \u6b21\u79fb\u52a8\u8d4b\u503c<\/td>\n2 \/ 0 \/ 1<\/td>\nvalue \u53ef\u9ed8\u8ba4\u6784\u9020，\u4e14\u4f60\u5c31\u662f\u8981\u8986\u76d6<\/td>\n<\/tr>\n
m.insert({k, v})<\/td>\n\u5ffd\u7565，bool=false<\/td>\n1<\/td>\n2 \u6b21\u79fb\u52a8<\/td>\n1 \/ 0 \/ 2<\/td>\n\u9700\u8981\u300c\u5230\u5e95\u63d2\u8fdb\u53bb\u4e86\u6ca1\u6709\u300d\u7684\u8fd4\u56de\u503c<\/td>\n<\/tr>\n
m.emplace(k, args…)<\/td>\n\u5ffd\u7565，\u4f46\u767d\u6784\u9020\u4e00\u4e2a<\/td>\n1（\u547d\u4e2d\u65f6\u4e5f\u6784\u9020）<\/td>\n0<\/td>\n1 \/ 0 \/ 0（dup \u4e5f\u662f 1）<\/td>\n\u65b0 key \u5c31\u5730\u6784\u9020；\u522b\u5bf9\u5df2\u5b58\u5728\u7684 key \u7528<\/td>\n<\/tr>\n
m.try_emplace(k, args…)<\/td>\n\u5ffd\u7565，\u4e14\u4e0d\u6784\u9020<\/td>\n1（\u547d\u4e2d\u65f6 0）<\/td>\n0<\/td>\n1 \/ 0 \/ 0（dup \u662f 0）<\/td>\nC++17 \u8d77\u7684\u65b0\u4ee3\u7801\u9996\u9009<\/td>\n<\/tr>\n
m.insert_or_assign(k, v)<\/td>\n\u8986\u76d6<\/td>\n1<\/td>\n1 \u6b21\u79fb\u52a8\u8d4b\u503c<\/td>\n1 \/ 0 \/ 1<\/td>\nC++17，\u8bed\u4e49\u4e0a\u660e\u786e\u8981\u8986\u76d6<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

\u4e09\u6761\u7ed3\u8bba：<\/p>\n

  • \u8981\u300c\u63d2\u5165，\u5df2\u5b58\u5728\u5c31\u522b\u52a8\u300d\u2192 \u7528 try_emplace\u3002 \u5b83\u662f\u552f\u4e00\u5728 key \u5df2\u5b58\u5728\u65f6\u8fde\u4e00\u4e2a\u5bf9\u8c61\u90fd\u4e0d\u6784\u9020\u7684\u5199\u6cd5（\u5b9e\u6d4b ctors=0），\u800c emplace \u5728\u540c\u6837\u60c5\u51b5\u4e0b\u767d\u6784\u9020\u4e00\u4e2a Widget \u518d\u9500\u6bc1（\u5b9e\u6d4b ctors=1）\u3002value \u5f88\u5927\u6216\u662f\u6301\u6709\u8d44\u6e90（\u6587\u4ef6\u53e5\u67c4\u3001unique_ptr）\u65f6，\u8fd9\u4e2a\u5dee\u522b\u5c31\u662f\u5b9e\u6253\u5b9e\u7684\u5f00\u9500\u3002<\/li>\n
  • operator[] \u7684\u4ee3\u4ef7\u662f\u300c\u9ed8\u8ba4\u6784\u9020 + \u8d4b\u503c\u300d\u4e24\u6b21\u64cd\u4f5c（\u5b9e\u6d4b ctors=2 moves=1），\u800c\u4e14\u8981\u6c42 value \u53ef\u9ed8\u8ba4\u6784\u9020\u3002\u5b83\u5728\u660e\u786e\u7684\u5199\u5165\u573a\u666f（m[k] = v\u3001m[k]++）\u591f\u7528，\u4f46\u4e0d\u8981\u7528\u5b83\u505a\u300c\u4e0d\u5b58\u5728\u624d\u63d2\u5165\u300d\u7684\u903b\u8f91\u3002<\/li>\n
  • \u8981\u300c\u8986\u76d6\u300d\u2192 \u7528 insert_or_assign，\u5b83\u7684\u610f\u56fe\u5199\u5728\u51fd\u6570\u540d\u91cc，\u6bd4 m[k] = v \u66f4\u660e\u786e；\u4e0d\u8fc7\u5b83\u8981\u6c42 value \u53ef\u8d4b\u503c\u2014\u2014\u6ce8\u610f\u4e0a\u9762\u4ee3\u7801\u91cc\u5199\u7684\u662f Widget{9}，\u76f4\u63a5\u5199 9 \u4f1a\u7f16\u8bd1\u5931\u8d25，\u56e0\u4e3a Widget \u7684\u5355\u53c2\u6784\u9020\u51fd\u6570\u662f explicit，\u4e0d\u5b58\u5728\u4ece int \u5230 Widget \u7684\u9690\u5f0f\u8d4b\u503c\u8f6c\u6362\u3002<\/li>\n

    insert \u7684\u8fd4\u56de\u503c std::pair<iterator, bool> \u503c\u5f97\u5355\u72ec\u8bb0\u4e00\u7b14：bool \u544a\u8bc9\u4f60\u300c\u5230\u5e95\u6709\u6ca1\u6709\u771f\u7684\u63d2\u5165\u300d，iterator \u6307\u5411\u300c\u73b0\u5728\u90a3\u4e2a key \u6240\u5728\u7684\u4f4d\u7f6e\u300d（\u4e0d\u7ba1\u662f\u65b0\u63d2\u7684\u8fd8\u662f\u672c\u6765\u5c31\u6709\u7684）\u3002\u4e0a\u9762\u7b2c 3 \u8282\u7684 insert("bob", 99) \u8f93\u51fa inserted=0 \u5c31\u662f\u8fd9\u4e2a boole \u5728\u8d77\u4f5c\u7528\u3002<\/p>\n

    \u5b98\u65b9\u6587\u6863：std::map::emplace \u2014 cppreference \u5b98\u65b9\u6587\u6863：std::map::try_emplace \u2014 cppreference \u5b98\u65b9\u6587\u6863：std::map::insert_or_assign \u2014 cppreference<\/p>\n

    \u8fd8\u6709\u4e00\u6761\u5fc5\u987b\u8bb0\u4f4f\u7684：map \u7684 key \u662f const\u3002value_type \u662f std::pair<const Key, T>，\u6240\u4ee5 it->second \u53ef\u4ee5\u6539，it->first \u6539\u4e0d\u4e86：<\/p>\n

    #<\/span>include<\/span> <map><\/span><\/span>
    \n#<\/span>include<\/span> <string><\/span><\/span><\/p>\n

    void<\/span> keys_are_const<\/span>(<\/span>std::<\/span>map<<\/span>int<\/span>,<\/span> std::<\/span>string><\/span>&<\/span> m)<\/span> {<\/span>
    \n auto<\/span> it =<\/span> m.<\/span>begin<\/span>(<\/span>)<\/span>;<\/span>
    \n it-><\/span>second =<\/span> "value is mutable"<\/span>;<\/span> \/\/ \u53ef\u4ee5：value \u975e const<\/span>
    \n \/\/ \u53cd\u4f8b，\u4e0d\u8981\u8fd9\u4e48\u5199：\u7f16\u8bd1\u5931\u8d25 \u2014\u2014 key_type \u662f const int<\/span>
    \n \/\/ it->first = 5; \/\/ error: assignment of read-only member<\/span>
    \n}<\/span><\/p>\n

    \u60f3\u6539 key，\u53ea\u80fd erase \u518d insert（\u8fd9\u6b63\u597d\u4e5f\u8bf4\u660e\u4e3a\u4ec0\u4e48 key \u4e0d\u80fd\u968f\u4fbf\u6539：\u6539\u4e86\u6811\u7684\u6709\u5e8f\u6027\u5c31\u5d29\u4e86）\u3002\u4e0a\u9762\u7684\u7247\u6bb5\u6545\u610f\u4e0d\u5199 main()，\u56e0\u4e3a\u5b83\u662f\u7528\u6765\u5c55\u793a\u7f16\u8bd1\u9519\u8bef\u7684\u3002<\/p>\n

    6. \u8303\u56f4\u67e5\u8be2\u4e0e\u81ea\u5b9a\u4e49\u6bd4\u8f83\u5668<\/h3>\n

    \u6709\u5e8f\u5bb9\u5668\u771f\u6b63\u8ba9\u4eba\u820d\u4e0d\u5f97\u653e\u5f03\u7684\u80fd\u529b\u662f\u8303\u56f4\u67e5\u8be2：lower_bound（\u7b2c\u4e00\u4e2a \u2265 key）\u3001upper_bound（\u7b2c\u4e00\u4e2a > key）\u3001equal_range（\u4e00\u6b21\u62ff\u5230\u4e24\u8005，\u4e5f\u5c31\u662f [lower_bound, upper_bound)）\u3002<\/p>\n

    \/\/ map_range.cpp \u2014 \u7f16\u8bd1: g++ -std=c++17 -Wall -O2 map_range.cpp -o map_range<\/span>
    \n#<\/span>include<\/span> <functional><\/span><\/span>
    \n#<\/span>include<\/span> <iostream><\/span><\/span>
    \n#<\/span>include<\/span> <iterator><\/span><\/span>
    \n#<\/span>include<\/span> <map><\/span><\/span>
    \n#<\/span>include<\/span> <string><\/span><\/span><\/p>\n

    \/\/ \u8e29\u5751\u7528\u7684\u6bd4\u8f83\u5668：\u53ea\u6309\u5b57\u7b26\u4e32\u957f\u5ea6\u6bd4\u8f83<\/span>
    \nstruct<\/span> ByLength<\/span> {<\/span>
    \n bool<\/span> operator<\/span>(<\/span>)<\/span>(<\/span>const<\/span> std::<\/span>string&<\/span> a,<\/span> const<\/span> std::<\/span>string&<\/span> b)<\/span> const<\/span> {<\/span>
    \n return<\/span> a.<\/span>size<\/span>(<\/span>)<\/span> <<\/span> b.<\/span>size<\/span>(<\/span>)<\/span>;<\/span>
    \n }<\/span>
    \n}<\/span>;<\/span><\/p>\n

    int<\/span> main<\/span>(<\/span>)<\/span> {<\/span>
    \n std::<\/span>map<<\/span>int<\/span>,<\/span> std::<\/span>string><\/span> m{<\/span>{<\/span>10<\/span>,<\/span> "ten"<\/span>}<\/span>,<\/span> {<\/span>20<\/span>,<\/span> "twenty"<\/span>}<\/span>,<\/span> {<\/span>30<\/span>,<\/span> "thirty"<\/span>}<\/span>,<\/span> {<\/span>40<\/span>,<\/span> "forty"<\/span>}<\/span>}<\/span>;<\/span><\/p>\n

    const<\/span> auto<\/span> lo =<\/span> m.<\/span>lower_bound<\/span>(<\/span>20<\/span>)<\/span>;<\/span> \/\/ \u7b2c\u4e00\u4e2a >= 20<\/span>
    \n const<\/span> auto<\/span> hi =<\/span> m.<\/span>upper_bound<\/span>(<\/span>30<\/span>)<\/span>;<\/span> \/\/ \u7b2c\u4e00\u4e2a > 30<\/span>
    \n std::<\/span>cout <<<\/span> "range [20, 30] :"<\/span>;<\/span>
    \n for<\/span> (<\/span>auto<\/span> it =<\/span> lo;<\/span> it !=<\/span> hi;<\/span> ++<\/span>it)<\/span> std::<\/span>cout <<<\/span> ' '<\/span> <<<\/span> it-><\/span>first <<<\/span> '='<\/span> <<<\/span> it-><\/span>second;<\/span>
    \n std::<\/span>cout <<<\/span> '\\\\n'<\/span>;<\/span><\/p>\n

    const<\/span> auto<\/span> [<\/span>first,<\/span> last]<\/span> =<\/span> m.<\/span>equal_range<\/span>(<\/span>30<\/span>)<\/span>;<\/span> \/\/ \u4e00\u6b21\u62ff\u5230\u4e0a\u4e0b\u754c<\/span>
    \n std::<\/span>cout <<<\/span> "equal_range(30) count = "<\/span> <<<\/span> std::<\/span>distance<\/span>(<\/span>first,<\/span> last)<\/span> <<<\/span> '\\\\n'<\/span>;<\/span><\/p>\n

    std::<\/span>map<<\/span>int<\/span>,<\/span> std::<\/span>string,<\/span> std::<\/span>greater<<\/span>int<\/span>>><\/span> desc{<\/span>{<\/span>10<\/span>,<\/span> "ten"<\/span>}<\/span>,<\/span> {<\/span>40<\/span>,<\/span> "forty"<\/span>}<\/span>,<\/span> {<\/span>20<\/span>,<\/span> "twenty"<\/span>}<\/span>}<\/span>;<\/span>
    \n std::<\/span>cout <<<\/span> "descending keys:"<\/span>;<\/span>
    \n for<\/span> (<\/span>const<\/span> auto<\/span>&<\/span> [<\/span>key,<\/span> value]<\/span> :<\/span> desc)<\/span> std::<\/span>cout <<<\/span> ' '<\/span> <<<\/span> key;<\/span>
    \n std::<\/span>cout <<<\/span> '\\\\n'<\/span>;<\/span><\/p>\n

    std::<\/span>multimap<<\/span>std::<\/span>string,<\/span> int<\/span>><\/span> scores{<\/span>{<\/span>"alice"<\/span>,<\/span> 80<\/span>}<\/span>,<\/span> {<\/span>"bob"<\/span>,<\/span> 90<\/span>}<\/span>,<\/span> {<\/span>"alice"<\/span>,<\/span> 95<\/span>}<\/span>}<\/span>;<\/span>
    \n const<\/span> auto<\/span> [<\/span>af,<\/span> al]<\/span> =<\/span> scores.<\/span>equal_range<\/span>(<\/span>"alice"<\/span>)<\/span>;<\/span>
    \n std::<\/span>cout <<<\/span> "alice scores:"<\/span>;<\/span>
    \n for<\/span> (<\/span>auto<\/span> it =<\/span> af;<\/span> it !=<\/span> al;<\/span> ++<\/span>it)<\/span> std::<\/span>cout <<<\/span> ' '<\/span> <<<\/span> it-><\/span>second;<\/span>
    \n std::<\/span>cout <<<\/span> '\\\\n'<\/span>;<\/span><\/p>\n

    std::<\/span>map<<\/span>std::<\/span>string,<\/span> int<\/span>,<\/span> ByLength><\/span> by_len;<\/span>
    \n by_len[<\/span>"ab"<\/span>]<\/span> =<\/span> 1<\/span>;<\/span>
    \n by_len[<\/span>"cd"<\/span>]<\/span> =<\/span> 2<\/span>;<\/span> \/\/ \u4e0e "ab" \u7b49\u4ef7（\u957f\u5ea6\u76f8\u540c）\u2192 \u4e0d\u65b0\u589e\u6761\u76ee<\/span>
    \n std::<\/span>cout <<<\/span> "by_len size = "<\/span> <<<\/span> by_len.<\/span>size<\/span>(<\/span>)<\/span>
    \n <<<\/span> " key = "<\/span> <<<\/span> by_len.<\/span>begin<\/span>(<\/span>)<\/span>-><\/span>first
    \n <<<\/span> " value = "<\/span> <<<\/span> by_len.<\/span>begin<\/span>(<\/span>)<\/span>-><\/span>second <<<\/span> '\\\\n'<\/span>;<\/span>
    \n return<\/span> 0<\/span>;<\/span>
    \n}<\/span><\/p>\n

    range [20, 30] : 20=twenty 30=thirty
    \nequal_range(30) count = 1
    \ndescending keys: 40 20 10
    \nalice scores: 80 95
    \nby_len size = 1 key = ab value = 2<\/p>\n

    \u9010\u4e2a\u770b：<\/p>\n

      \n
    • [lower_bound(20), upper_bound(30)) \u6070\u597d\u662f [20, 30]：\u4e0b\u534a\u754c\u662f\u95ed\u3001\u4e0a\u534a\u754c\u662f\u5f00，\u6240\u4ee5\u60f3\u8981\u300c\u542b 30\u300d\u5c31\u5fc5\u987b\u7528 upper_bound(30) \u800c\u4e0d\u662f lower_bound(30)\u3002\u8fd9\u4e2a\u534a\u5f00\u533a\u95f4\u7ea6\u5b9a\u548c STL \u5176\u4ed6\u7b97\u6cd5\u4e00\u81f4\u3002<\/li>\n
    • equal_range \u4e00\u6b21\u8fd4\u56de\u4e0a\u4e0b\u754c，\u7528 std::distance \u6570\u4e00\u4e0b\u5c31\u662f\u300c\u8fd9\u4e2a key \u6709\u51e0\u4e2a\u5143\u7d20\u300d\u3002map \u91cc\u6700\u591a 1 \u4e2a，multimap \u91cc\u53ef\u4ee5\u591a\u4e2a\u2014\u2014\u6240\u4ee5 equal_range \u914d multimap \u6700\u5408\u9002（\u793a\u4f8b\u91cc alice \u7684 80 \u548c 95 \u90fd\u62ff\u5230\u4e86）\u3002<\/li>\n
    • \u6362\u6bd4\u8f83\u5668\u5c31\u6362\u4e86\u904d\u5386\u987a\u5e8f：std::greater<int> \u8ba9 key \u964d\u5e8f，\u8fd9\u662f\u300c\u6709\u5e8f\u300d\u7684\u53e6\u4e00\u4e2a\u7528\u6cd5\u3002<\/li>\n
    • \u6700\u540e\u4e00\u6bb5\u662f\u8e29\u5751\u793a\u8303：ByLength \u53ea\u6bd4\u5b57\u7b26\u4e32\u957f\u5ea6，\u4e8e\u662f "ab" \u548c "cd" \u5728\u5b83\u773c\u91cc\u7b49\u4ef7（\u8c01\u90fd\u4e0d\u5c0f\u4e8e\u8c01），map \u8ba4\u4e3a\u5b83\u4eec\u662f\u540c\u4e00\u4e2a key\u2014\u2014by_len["cd"] = 2 \u6839\u672c\u6ca1\u65b0\u589e\u6761\u76ee，\u53ea\u662f\u628a "ab" \u90a3\u683c\u7684\u503c\u6539\u6210\u4e86 2\u3002\u8f93\u51fa by_len size = 1 key = ab value = 2 \u8bc1\u5b9e\u4e86\u8fd9\u4e00\u70b9\u3002<\/li>\n<\/ul>\n

      \u89c4\u5219：\u81ea\u5b9a\u4e49\u6bd4\u8f83\u5668\u5fc5\u987b\u662f\u4e00\u4e2a\u4e25\u683c\u5f31\u5e8f（strict weak ordering），\u5176\u4e2d\u6700\u5bb9\u6613\u88ab\u5ffd\u7565\u7684\u4e00\u6761\u662f\u300c\u7b49\u4ef7\u5fc5\u987b\u53ef\u4f20\u9012\u300d\u2014\u2014comp(a,b)==false && comp(b,a)==false \u7684\u4e24\u4e2a key \u4f1a\u88ab\u5f53\u4f5c\u540c\u4e00\u4e2a key\u3002\u53ea\u6bd4\u4e00\u90e8\u5206\u5b57\u6bb5（\u957f\u5ea6\u3001\u5927\u5c0f\u5199\u5ffd\u7565\u540e\u7684\u6837\u5b50\u3001float \u7684\u8fd1\u4f3c\u76f8\u7b49）\u662f\u5f88\u5371\u9669\u7684\u6bd4\u8f83\u5668\u3002\u9ed8\u8ba4\u7684 std::less<Key>（\u5373 operator<）\u5728\u7edd\u5927\u591a\u6570\u573a\u666f\u90fd\u662f\u5bf9\u7684\u3002<\/p>\n

      \u5b98\u65b9\u6587\u6863：std::map::lower_bound \u2014 cppreference \u5b98\u65b9\u6587\u6863：std::lower_bound（\u6cdb\u578b\u7b97\u6cd5）\u2014 cppreference \u5b98\u65b9\u6587\u6863：std::less \u2014 cppreference：std::map \u7684\u9ed8\u8ba4\u6bd4\u8f83\u5668，\u8bed\u4e49\u5c31\u662f operator<\u3002<\/p>\n

      7. \u5b8c\u6574\u793a\u4f8b：\u4e00\u4efd\u6709\u5e8f\u7684\u6210\u7ee9\u5355<\/h3>\n

      \u4e0b\u9762\u8fd9\u4e2a\u4f8b\u5b50\u628a\u524d\u9762\u6240\u6709\u8981\u70b9\u4e32\u8d77\u6765：insert \u7684 bool \u5224\u91cd\u3001multimap \u6309\u5206\u6570\u6392\u5e8f\u53d6 Top-N\u3001lower_bound\/upper_bound \u505a\u5206\u6570\u533a\u95f4\u67e5\u8be2\u3002Key（\u59d3\u540d）\u7528 map \u4fdd\u8bc1\u4e0d\u91cd\u590d\u4e14\u6709\u5e8f；\u5206\u6570\u662f\u300c\u4e00\u5bf9\u591a\u300d\u7684，\u6240\u4ee5\u6392\u5e8f\u8f93\u51fa\u7528 multimap\u3002<\/p>\n

      \/\/ score_board.cpp \u2014 \u7f16\u8bd1: g++ -std=c++17 -Wall -O2 score_board.cpp -o score_board<\/span>
      \n#<\/span>include<\/span> <cstddef><\/span><\/span>
      \n#<\/span>include<\/span> <functional><\/span><\/span>
      \n#<\/span>include<\/span> <iostream><\/span><\/span>
      \n#<\/span>include<\/span> <map><\/span><\/span>
      \n#<\/span>include<\/span> <string><\/span><\/span>
      \n#<\/span>include<\/span> <vector><\/span><\/span><\/p>\n

      class<\/span> ScoreBoard<\/span> {<\/span>
      \npublic<\/span>:<\/span>
      \n void<\/span> add<\/span>(<\/span>const<\/span> std::<\/span>string&<\/span> name,<\/span> int<\/span> score)<\/span> {<\/span>
      \n const<\/span> auto<\/span> [<\/span>it,<\/span> inserted]<\/span> =<\/span> scores_.<\/span>insert<\/span>(<\/span>{<\/span>name,<\/span> score}<\/span>)<\/span>;<\/span>
      \n if<\/span> (<\/span>!<\/span>inserted)<\/span> {<\/span>
      \n it-><\/span>second =<\/span> score;<\/span> \/\/ \u5df2\u5b58\u5728\u5c31\u66f4\u65b0\u5206\u6570（key \u4e0d\u53ef\u6539，value \u53ef\u6539）<\/span>
      \n }<\/span>
      \n }<\/span><\/p>\n

      std::<\/span>vector<<\/span>std::<\/span>string><\/span> top<\/span>(<\/span>std::<\/span>size_t count)<\/span> const<\/span> {<\/span>
      \n std::<\/span>multimap<<\/span>int<\/span>,<\/span> std::<\/span>string,<\/span> std::<\/span>greater<<\/span>int<\/span>>><\/span> ranked;<\/span> \/\/ \u5206\u6570\u4ece\u9ad8\u5230\u4f4e<\/span>
      \n for<\/span> (<\/span>const<\/span> auto<\/span>&<\/span> [<\/span>name,<\/span> score]<\/span> :<\/span> scores_)<\/span> ranked.<\/span>insert<\/span>(<\/span>{<\/span>score,<\/span> name}<\/span>)<\/span>;<\/span>
      \n std::<\/span>vector<<\/span>std::<\/span>string><\/span> result;<\/span>
      \n for<\/span> (<\/span>const<\/span> auto<\/span>&<\/span> [<\/span>score,<\/span> name]<\/span> :<\/span> ranked)<\/span> {<\/span>
      \n if<\/span> (<\/span>result.<\/span>size<\/span>(<\/span>)<\/span> ==<\/span> count)<\/span> break<\/span>;<\/span>
      \n result.<\/span>push_back<\/span>(<\/span>name)<\/span>;<\/span>
      \n }<\/span>
      \n return<\/span> result;<\/span>
      \n }<\/span><\/p>\n

      std::<\/span>vector<<\/span>std::<\/span>string><\/span> between<\/span>(<\/span>int<\/span> low,<\/span> int<\/span> high)<\/span> const<\/span> {<\/span>
      \n std::<\/span>multimap<<\/span>int<\/span>,<\/span> std::<\/span>string><\/span> sorted;<\/span> \/\/ \u9ed8\u8ba4 less：\u5347\u5e8f，\u624d\u80fd\u505a\u533a\u95f4\u67e5\u8be2<\/span>
      \n for<\/span> (<\/span>const<\/span> auto<\/span>&<\/span> [<\/span>name,<\/span> score]<\/span> :<\/span> scores_)<\/span> sorted.<\/span>insert<\/span>(<\/span>{<\/span>score,<\/span> name}<\/span>)<\/span>;<\/span>
      \n std::<\/span>vector<<\/span>std::<\/span>string><\/span> result;<\/span>
      \n const<\/span> auto<\/span> last =<\/span> sorted.<\/span>upper_bound<\/span>(<\/span>high)<\/span>;<\/span> \/\/ \u4e0a\u534a\u754c\u5f00，\u624d\u5305\u542b high<\/span>
      \n for<\/span> (<\/span>auto<\/span> it =<\/span> sorted.<\/span>lower_bound<\/span>(<\/span>low)<\/span>;<\/span> it !=<\/span> last;<\/span> ++<\/span>it)<\/span> {<\/span>
      \n result.<\/span>push_back<\/span>(<\/span>it-><\/span>second)<\/span>;<\/span>
      \n }<\/span>
      \n return<\/span> result;<\/span>
      \n }<\/span><\/p>\n

      std::<\/span>size_t size<\/span>(<\/span>)<\/span> const<\/span> {<\/span> return<\/span> scores_.<\/span>size<\/span>(<\/span>)<\/span>;<\/span> }<\/span><\/p>\n

      private<\/span>:<\/span>
      \n std::<\/span>map<<\/span>std::<\/span>string,<\/span> int<\/span>><\/span> scores_;<\/span> \/\/ \u6309\u4eba\u540d\u6709\u5e8f，\u4fbf\u4e8e\u67e5\u627e<\/span>
      \n}<\/span>;<\/span><\/p>\n

      int<\/span> main<\/span>(<\/span>)<\/span> {<\/span>
      \n ScoreBoard board;<\/span>
      \n board.<\/span>add<\/span>(<\/span>"alice"<\/span>,<\/span> 80<\/span>)<\/span>;<\/span>
      \n board.<\/span>add<\/span>(<\/span>"bob"<\/span>,<\/span> 95<\/span>)<\/span>;<\/span>
      \n board.<\/span>add<\/span>(<\/span>"carol"<\/span>,<\/span> 70<\/span>)<\/span>;<\/span>
      \n board.<\/span>add<\/span>(<\/span>"dave"<\/span>,<\/span> 88<\/span>)<\/span>;<\/span>
      \n board.<\/span>add<\/span>(<\/span>"alice"<\/span>,<\/span> 92<\/span>)<\/span>;<\/span> \/\/ \u91cd\u540d -> \u66f4\u65b0\u5206\u6570，\u4e0d\u65b0\u589e\u6761\u76ee<\/span><\/p>\n

      std::<\/span>cout <<<\/span> "players = "<\/span> <<<\/span> board.<\/span>size<\/span>(<\/span>)<\/span> <<<\/span> '\\\\n'<\/span>;<\/span>
      \n std::<\/span>cout <<<\/span> "top 3:"<\/span>;<\/span>
      \n for<\/span> (<\/span>const<\/span> std::<\/span>string&<\/span> name :<\/span> board.<\/span>top<\/span>(<\/span>3<\/span>)<\/span>)<\/span> std::<\/span>cout <<<\/span> ' '<\/span> <<<\/span> name;<\/span>
      \n std::<\/span>cout <<<\/span> '\\\\n'<\/span>;<\/span>
      \n std::<\/span>cout <<<\/span> "score in [80, 95]:"<\/span>;<\/span>
      \n for<\/span> (<\/span>const<\/span> std::<\/span>string&<\/span> name :<\/span> board.<\/span>between<\/span>(<\/span>80<\/span>,<\/span> 95<\/span>)<\/span>)<\/span> std::<\/span>cout <<<\/span> ' '<\/span> <<<\/span> name;<\/span>
      \n std::<\/span>cout <<<\/span> '\\\\n'<\/span>;<\/span>
      \n return<\/span> 0<\/span>;<\/span>
      \n}<\/span><\/p>\n

      players = 4
      \ntop 3: bob alice dave
      \nscore in [80, 95]: dave alice bob<\/p>\n

      players = 4 \u800c\u4e0d\u662f 5，\u8bf4\u660e\u91cd\u540d\u7684 alice \u8d70\u4e86\u300c\u66f4\u65b0\u300d\u5206\u652f；top 3 \u6309\u5206\u6570\u964d\u5e8f\u7ed9\u51fa bob(95)\u3001alice(92)\u3001dave(88)；\u533a\u95f4\u67e5\u8be2\u6309\u5206\u6570\u5347\u5e8f\u7ed9\u51fa dave(88)\u3001alice(92)\u3001bob(95)\u3002\u56db\u4e2a\u5bb9\u5668（map \/ multimap \u00d7 \u4e24\u79cd\u6bd4\u8f83\u5668）\u5404\u53f8\u5176\u804c\u3002<\/p>\n

      8. \u9009\u578b\u901f\u67e5<\/h3>\n\n\u9700\u6c42\u9009\u8c01\u7406\u7531<\/tr>\n\n\n\n\n\n\n\n\n\n
      \u952e\u503c\u6620\u5c04 + \u9700\u8981\u6709\u5e8f\u904d\u5386<\/td>\nstd::map<\/td>\n\u7ea2\u9ed1\u6811，O(log n) \u4e14 key \u6709\u5e8f<\/td>\n<\/tr>\n
      \u53bb\u91cd + \u6709\u5e8f<\/td>\nstd::set<\/td>\n\u540c\u4e0a，\u53ea\u5b58 key<\/td>\n<\/tr>\n
      \u4e00\u5bf9\u591a\u4e14\u8981\u6709\u5e8f<\/td>\nstd::multimap \/ std::multiset<\/td>\n\u5141\u8bb8\u7b49\u4ef7 key，equal_range \u62ff\u5230\u5168\u90e8<\/td>\n<\/tr>\n
      \u53ea\u5224\u65ad\u5b58\u5728\u6027<\/td>\nfind \/ count（C++20 \u7528 contains）<\/td>\n\u522b\u7528 operator[]，\u5b83\u4f1a\u63d2\u5165<\/td>\n<\/tr>\n
      \u300c\u4e0d\u5b58\u5728\u624d\u63d2\u5165\u300d<\/td>\ntry_emplace（C++17）<\/td>\n\u547d\u4e2d\u65f6\u4e0d\u6784\u9020\u4efb\u4f55\u5bf9\u8c61<\/td>\n<\/tr>\n
      \u300c\u5b58\u5728\u5c31\u8986\u76d6\u300d<\/td>\ninsert_or_assign（C++17）<\/td>\n\u8bed\u4e49\u660e\u786e，\u4e14\u8fd4\u56de\u662f\u5426\u4e3a\u65b0\u63d2\u5165<\/td>\n<\/tr>\n
      \u53ea\u9700\u8981 O(1) \u5e73\u5747\u67e5\u627e\u3001\u4e0d\u5728\u4e4e\u987a\u5e8f<\/td>\nstd::unordered_map<\/td>\n\u54c8\u5e0c\u8868，\u89c1\u300aunordered_map \/ unordered_set \u5b8c\u5168\u6307\u5357\u300b<\/td>\n<\/tr>\n
      \u5143\u7d20\u5f88\u5c11（\u5341\u51e0\u4e2a）<\/td>\nstd::vector + \u6392\u5e8f<\/td>\n\u5c0f N \u65f6\u7ebf\u6027\u67e5\u627e\u7684\u5e38\u6570\u56e0\u5b50\u6bd4\u6811\u66f4\u4f4e<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

      9. \u5ef6\u4f38\u9605\u8bfb<\/h3>\n
        \n
      • std::map \u2014 cppreference：\u63a5\u53e3\u5168\u8c8c；\u6ce8\u610f value_type \u662f pair<const Key, T>，\u8fd9\u5c31\u662f key \u4e0d\u53ef\u6539\u7684\u6765\u6e90\u3002<\/li>\n
      • std::map::operator[] \u2014 cppreference：\u5b98\u65b9\u660e\u786e\u5199\u4e86\u300ckey \u4e0d\u5b58\u5728\u65f6\u63d2\u5165 value-initialized \u7684 value\u300d，\u662f\u7b2c 3 \u8282\u7684\u4f9d\u636e\u3002<\/li>\n
      • std::map::try_emplace \u2014 cppreference：\u6ce8\u610f\u300c\u82e5 key \u5df2\u5b58\u5728\u5219\u4e0d\u505a\u4efb\u4f55\u4e8b\u300d\u8fd9\u53e5，\u662f\u5b83\u6bd4 emplace \u7701\u7684\u6839\u6e90\u3002<\/li>\n
      • std::map::lower_bound \u2014 cppreference \u4e0e std::map::upper_bound：\u534a\u5f00\u533a\u95f4\u7684\u5b98\u65b9\u5b9a\u4e49，\u914d\u5408 equal_range \u4e00\u8d77\u770b\u3002<\/li>\n
      • std::multimap \u2014 cppreference：\u7b49\u4ef7 key \u7684\u76f8\u90bb\u6027\u4fdd\u8bc1（\u540c\u4e00\u4e2a key \u7684\u5143\u7d20\u5728\u904d\u5386\u4e2d\u8fde\u7eed\u51fa\u73b0）\u3002<\/li>\n
      • C++ Core Guidelines \u2014 isocpp.github.io：\u5bb9\u5668\u9009\u578b\u4e0e\u300c\u522b\u7528 operator[] \u505a\u67e5\u8be2\u300d\u8fd9\u7c7b\u63a5\u53e3\u8bbe\u8ba1\u601d\u8def\u7684\u6765\u6e90\u3002<\/li>\n<\/ul>\n

        10. \u4e00\u53e5\u8bdd\u603b\u7ed3<\/h3>\n

        std::map \/ std::set \u662f\u4e00\u68f5\u7ea2\u9ed1\u6811，\u6709\u5e8f\u548c O(log n) \u662f\u540c\u4e00\u5957\u7ed3\u6784\u7684\u4e24\u4e2a\u7ed3\u679c：\u4e2d\u5e8f\u904d\u5386\u5373\u6709\u5e8f，\u6240\u4ee5\u6709 lower_bound\/upper_bound\/equal_range；\u6811\u9ad8\u88ab\u4fdd\u8bc1\u5728 O(log n)，\u6240\u4ee5 map::find \u67e5 1000 \u4e2a key \u53ea\u8981 11 \u6b21\u6bd4\u8f83，\u800c std::find_if \u8981\u626b 501 \u6b21\u3002\u7528\u4e4b\u524d\u8bb0\u4f4f\u4e09\u6761：operator[] \u627e\u4e0d\u5230\u4f1a\u63d2\u5165\u9ed8\u8ba4\u503c，\u53ea\u8bfb\u67e5\u8be2\u7528 find（\u8981\u629b\u5f02\u5e38\u7528 at，C++20 \u53ef contains）；\u63d2\u5165\u7528 try_emplace，\u5b83\u662f\u552f\u4e00\u5728 key \u5df2\u5b58\u5728\u65f6\u4e0d\u6784\u9020\u4efb\u4f55\u5bf9\u8c61\u7684\u5199\u6cd5（emplace \u4f1a\u767d\u6784\u9020\u4e00\u4e2a）；key \u662f const，\u4e14\u81ea\u5b9a\u4e49\u6bd4\u8f83\u5668\u5fc5\u987b\u6ee1\u8db3\u4e25\u683c\u5f31\u5e8f，\u5426\u5219\u300c\u7b49\u4ef7\u300d\u7684 key \u4f1a\u88ab\u6084\u6084\u541e\u6389\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"

        std::map \u662f C \u91cc\u6700\u5e38\u88ab\u7528\u3001\u4e5f\u6700\u5bb9\u6613\u88ab\u7528\u9519\u7684\u5bb9\u5668\u3002\u5b83\u7684\u6838\u5fc3\u4e8b\u5b9e\u53ea\u6709\u4e00\u53e5\u8bdd：\u5b83\u662f\u4e00\u68f5\u81ea\u5e73\u8861\u7684\u7ea2\u9ed1\u6811（red-black tree），\u6240\u4ee5 key \u6c38\u8fdc\u6709\u5e8f\u3001\u67e5\u627e\u6c38\u8fdc\u662f O(log n)\u3002\u6709\u5e8f\u5e26\u6765\u8303\u56f4\u67e5\u8be2\u3001\u4e2d\u5e8f\u904d\u5386\u5373\u6392\u5e8f\u3001find \u4f18\u4e8e std::find \u8fd9\u4e9b\u80fd\u529b；\u4f46\u4e5f\u5e26\u6765\u4e00\u4e2a\u8457\u540d\u9677\u9631\u2014\u2014operator[] \u5728\u627e\u4e0d\u5230 key \u65f6\u4f1a\u9ed8\u9ed8\u63d2\u5165\u4e00\u4e2a\u9ed8\u8ba4\u503c\u3002\u8fd9\u7bc7\u6309\u300c\u7ed3\u6784 \u2192 \u53ea\u8bfb\u67e5\u8868 \u2192 \u67e5\u627e\u5199\u6cd5 \u2192 \u63d2<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[12806,55,3759,56,1813],"topic":[],"class_list":["post-112625","post","type-post","status-publish","format-standard","hentry","category-server","tag-12806","tag-c","tag-stl","tag-56","tag-1813"],"yoast_head":"\nmap \/ set \u5b8c\u5168\u6307\u5357\uff1a\u7ea2\u9ed1\u6811\u4e0e\u6709\u5e8f\u5bb9\u5668 - 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