Leetcode 76. 最小覆盖子串 (双指针，map)

输入: S = "ADOBECODEBANC", T = "ABC"
输出: "BANC"

class Solution {
public:
    string minWindow(string s, string t) {
        unordered_map<char,int>p;
        for(char c:t)p[c]++;
        int k=p.size();
        int st=0,len=INT_MAX,cnt=0;
        for(int i=0,j=0,cnt=0;s[i];i++)
        {
            if(p[s[i]]==1)cnt++;
            p[s[i]]--;
            while(p[s[j]]<0)p[s[j++]]++;
            if(cnt==k)
            {
                if(len>i-j+1)
                {
                    len=i-j+1;
                    st=j;
                }
            }
            //cout<<cnt<<endl;
        }
        return len==INT_MAX?"":s.substr(st,len);
    }
};