题目：

题解：

char* minWindow(char* s, char* t) {
    int tLen = strlen(t);
    int hash[256] = { 0 };
    for (int i = 0; i < tLen; ++i)
        ++hash[t[i]];
    for (int i = 0; i < 256; ++i) {
        if (0 == hash[i])
            hash[i] = INT_MIN;
    }
    
    int left, right, count, start, minLen, sLen;
    left = right = count = 0;
    start = -1;
    minLen = INT_MAX;
    sLen = strlen(s);
    for (right; right < sLen; ++right) {
        if (hash[s[right]] > INT_MIN) {
            if (hash[s[right]] > 0)
                ++count;
            --hash[s[right]];
        }
        
        if (count == tLen) {
            while (hash[s[left]] < 0) {
                if (hash[s[left]] > INT_MIN)
                    ++hash[s[left]];
                ++left;
            }
            if (right - left + 1 < minLen) {
                minLen = right - left + 1;
                start = left;
            }
            ++hash[s[left]];
            ++left;
            --count; //注意只丢弃第一个字符
        }
    }

    if (start == -1) {
        char* ans = (char*)malloc(sizeof(char));
        if (ans) {
            *ans = '\0';
            return ans;
        }
    }
    else {
        char* ans = (char*)malloc(sizeof(char) * minLen + 1);
        if (ans) {
            int i = 0, j = start;
            for (i; i < minLen; ++i) {
                ans[i] = s[j];
                ++j;
            }
            ans[minLen] = '\0';
            return ans;
        }
    }
    return NULL;
}