LeetCode Minimum Window Substring

最新推荐文章于 2012-11-24 01:43:33 发布

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本文介绍了一个寻找字符串S中包含字符串T所有字符的最小子串的问题，并提供了一个C++实现的解决方案。通过使用滑动窗口技术和哈希映射，该算法能在O(n)的时间复杂度内找到满足条件的最小子串。

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Minimum Window Substring

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 emtpy string "".

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

Tips:

Maybe a int[256] is a better choice to replace map<char,int>

Solution:

class Solution {
public:
    string minWindow(string S, string T) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        sort(T.begin(),T.end());
        map<char,int> count;
        int total=T.size();
        for(int i=0;i<T.size();++i){
            ++count[T[i]];
        }
        int start=0,end=0;
        int len=S.size(),minstart=0;
        for(int i=0;i<S.size();++i){
            ++end;
            if(count.find(S[i])!=count.end()){
                if(count[S[i]]-->0)
                    --total;
            }
            while(total==0&&start<end&&(count.find(S[start])==count.end()||
                    count[S[start]]<0)){
                if(count.find(S[start])!=count.end())
                    ++count[S[start]];
                ++start;
            }
            if(total==0&&end-start<len){
                minstart=start;
                len=end-start;
            }
        }
        return total==0?S.substr(minstart,len):string("");
    }
};