\u8003\u8651\u5230dp[i] = dp[i] – 1 – dp[ind-1]\u53ef\u80fd<0，\u6240\u4ee5\u9700\u8981\u52a0\u4e0a\u6a211e9+7<\/p>\n
![\"image.png\"](\"https:\/\/www.wsisp.com\/helps\/wp-content\/uploads\/2026\/02\/20260209235806-698a748e58518.png\")
<\/p>\n
Code<\/h2>\n
class Solution {
\npublic:
\n int ch[26];
\n const long long modulo = 1e9 + 7;
\n int distinctSubseqII(string s) {
\n fill(ch, ch + 26, -1);
\n int n = s.size(), ind;
\n if(n==1) return 1;
\n vector<long long> dp(n, 0);
\n dp[0] = 1;
\n ch[s[0]-'a'] = 0;
\n for(int i = 1; i < n; i++) {
\n dp[i] = (dp[i-1] << 1) + 1;
\n ind = ch[s[i]-'a'];
\n if(ind == 0) {
\n dp[i] = dp[i] – 1 + modulo;
\n } else if(ind > 0){
\n dp[i] = dp[i] – 1 – dp[ind-1] + modulo;
\n }
\n ch[s[i]-'a'] = i;
\n dp[i] = dp[i] % modulo;
\n }
\n int ret = dp[n-1] % modulo;
\n return ret;
\n }
\n};<\/p>\n","protected":false},"excerpt":{"rendered":"
Problem: 940. Distinct Subsequences II \u4e0d\u540c\u7684\u5b50\u5e8f\u5217 II \u8017\u65f6100%，\u52a8\u6001\u89c4\u5212\u7684，\u8003\u8651\u4e24\u79cd\u60c5\u51b5，\u6bcf\u79cd\u5b57\u7b26\u90fd\u4e0d\u76f8\u540c，\u5b58\u5728\u76f8\u540c\u7684\u5b57\u7b26，dp[i]\u8868\u793as[0～i]\u5b50\u5b57\u7b26\u4e32\u7684\u603b\u6570，\u82e5\u662fs[0~i-1]\u4e0d\u5b58\u5728s[i]，\u90a3\u4e48\u7ed3\u679c\u5c31\u662fdp[i] (dp[i-1] * 2) 1;\u4e5f\u5c31\u662f\u4e4b\u524d\u7684\u6240\u6709\u5b50\u5b57\u7b26\u4e32\u6700\u540e\u9762\u52a0\u4e0as[i]\u5373\u53ef࿰<\/p>\n","protected":false},"author":2,"featured_media":74593,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[2692,427,925],"topic":[],"class_list":["post-74594","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-server","tag-leetcode","tag-427","tag-925"],"yoast_head":"\n