LeetCode.76. 最小覆盖子串

题目

思路

滑动窗口+need数组，同438题

代码

string minWindow(string s, string t) 
{
    auto m = t.size();
    auto n = s.size();

    vector<int> need(123,0);
    int needCnt = m;
    for(const char& c:t)
    {
        need[c]++;
    }
    int R = 0, L = 0;
    int stIndx = -1;
    int minLen = n;
    while(R<n)
    {
        char c = s[R];
        R++;
        if(need[c] > 0)
        {
            needCnt--;
        }
        need[c]--;
        if(needCnt == 0)
        {
            while(L<R && need[s[L]] < 0)//收缩左端点，看有没有多余的元素(need[] < 0)
            {
                need[s[L]]++;
                L++;
            }
            int curLen = R-L;
            if(curLen <= minLen)// 需要 = ，应对 s,t俩字符串相同的情况 "ABC"  "ABC"，此时curLen == n
            {
                minLen = curLen;
                stIndx = L; 
            }
        }
    }
    cout << "stIndx = " << stIndx;
    return stIndx == -1 ? "" : s.substr(stIndx,minLen);
}