74th LeetCode Weekly Contest Valid Number of Matching Subsequences

Given string S and a dictionary of words words, find the number of words[i] that is a subsequence of S.

Example :
Input: 
S = "abcde"
words = ["a", "bb", "acd", "ace"]
Output: 3
Explanation: There are three words in words that are a subsequence of S: "a", "acd", "ace".

Note:

• All words in words and S will only consists of lowercase letters.
• The length of S will be in the range of [1, 50000].
• The length of words will be in the range of [1, 5000].
• The length of words[i] will be in the range of [1, 50].

问S中有多少符合words里面的单词（可以不连续哦）

当然是二分啊，我们保存S中字母的位置，对于每个words我们都查找字母的位置，然后+1一位继续找

class Solution {
public:
    int numMatchingSubseq(string S, vector<string>& words) {
        int num=0;
        vector<int>vec[50000];
        int len=S.size();
        for(int i=0;i<len;i++){
            vec[S[i]-'a'].push_back(i);
        }
        for(auto word:words){
            int add=0;
            int wordLen=word.size();
            int flag=1;
           // cout<<word<<endl;
            for(int i=0;i<wordLen;i++){
                if(vec[word[i]-'a'].size()==0){
                    flag=0;
                    break;
                }
                auto it=lower_bound(vec[word[i]-'a'].begin(),vec[word[i]-'a'].end(),add);
                if(it==vec[word[i]-'a'].end()){
                    flag=0;
                    break;
                }
                add=(*it);
                add++;
              //  cout<<add<<endl;
            }
            if(flag){
                num++;
            }
        }
        return num;
    }
};