LeetCode76 Minimum Window Substring 最小窗口子串 C++

最新推荐文章于 2022-04-12 22:33:27 发布

原创最新推荐文章于 2022-04-12 22:33:27 发布 · 323 阅读

0 ·

CC 4.0 BY-SA版权

LeetCode 专栏收录该内容

503 篇文章

订阅专栏

本文介绍了一种在字符串S中寻找包含字符串T所有字符的最短子串的算法，复杂度为O(n)。通过使用哈希表进行快速查找，确保了算法的高效运行。

问题描述：
Given a string S and a string T, find the minimum window in S which will contain all the characters in T in complexity O(n).

Example:

Input: S = "ADOBECODEBANC", T = "ABC"
Output: "BANC"

Note:

If there is no such window in S that covers all characters in T, return the empty string “”.
If there is such window, you are guaranteed that there will always be only one unique minimum window in S.
题源：here；完整实现：here
思路：
推荐参考文献（here），其简洁性让人信服。同样这道题为了达到快速查找的目的使用了hash表，代码如下：

    string minWindow(string s, string t) {
        unordered_map<char, int> hash;
        int left = 0, len = INT_MAX, num = t.size(), start = 0;
        for (auto val : t) hash[val]++;
        for (int i = 0; i < s.size();i++){
            if (hash[s[i]]-- > 0) num--;
            while (num == 0){
                len = len < (i - left + 1) ? len : i - (start = left) + 1;
                if (hash[s[left++]]++ == 0) num++;
            }
        }

        return len == INT_MAX ? "" : s.substr(start, len);
    }