LeetCode (Minimum Window Substring)

最新推荐文章于 2019-08-22 03:21:47 发布

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最新推荐文章于 2019-08-22 03:21:47 发布

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分类专栏： C++

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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)。通过使用计数器和映射表的方法，确保了高效的查找过程，并给出了具体的实现代码。

Problem:

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).

For example,
S = "ADOBECODEBANC"
T = "ABC"

Minimum window is "BANC".

Note:
If there is no such window in S that covers all characters in T, return the empty string "".

If there are multiple such windows, you are guaranteed that there will always be only one unique minimum window in S.

Solution:

class Solution {
public:
    string minWindow(string s, string t) {
        vector<int> map(128, 0);
        for(auto c : t) map[c]++;
        int counter = t.size(), l = INT_MAX;
        int begin = 0, end = 0, head = 0;
        while(end < s.size()){
            if(map[s[end++]]-- > 0) counter--;
            while(counter == 0){
                if(end - begin < l) l = end - (head = begin);
                if(map[s[begin++]]++ == 0) counter++;
            }
        }
        return l == INT_MAX ? "" : s.substr(head, l);
    }
};