Leetcode: Minimum Window Substring

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兩個指標+字元hash

string minWindow(string S, string T) {        // Start typing your C/C++ solution below        // DO NOT write int main() function        int nT = T.size();        int nS = S.size();                int needToFind[256] = {0};        for (int i = 0; i < nT; ++i)            ++needToFind[T[i]];        int hasFound[256] = {0};        int minBegin;        int minEnd;        int minWindow = nS + 1;        int count = 0;                char ch;        for (int begin = 0, end = 0; end < nS; ++end)        {            if (needToFind[S[end]] == 0)                continue;            ch = S[end];            ++hasFound[ch];            if (hasFound[ch] <= needToFind[ch])                ++count;                            if (count == nT)            {                while (needToFind[S[begin]] == 0                || hasFound[S[begin]] > needToFind[S[begin]])                {                    if (hasFound[S[begin]] > needToFind[S[begin]])                        --hasFound[S[begin]];                    ++begin;                }                                int length = end - begin + 1;                if (length < minWindow)                  {                    minBegin = begin;                    minEnd = end;                    minWindow = length;                }            }        }                return minWindow <= nS ? S.substr(minBegin, minEnd-minBegin+1) : "";    }