leetcode 76. 最小覆盖子串

代码

class Solution {
public:
    string minWindow(string s, string t) {
        string res = "";
        int m[128] = { 0 };             //哈希数组
        int left = 0, right = 0, need = t.size(), minstart = 0, minlen = INT_MAX;
        for(char c : t)     
            ++m[c];         //记录t中字符出现次数
        while(right < s.size())
        {
            if(m[s[right]] > 0)    --need;         //窗口右移，每包含一个t中的字符，need--
            --m[s[right]];
            ++right;
            while(need == 0)            //当t中的字符全部被包含在[left,right]时
            {
                if(right - left < minlen)
                {
                    minstart = left;
                    minlen = right - left;
                }
                ++m[s[left]];                       //窗口左移
                if(m[s[left]] > 0)  ++need;
                ++left;
            }
        }
        if(minlen != INT_MAX)   res = s.substr(minstart , minlen);
        return res;
    }
};