算法描述：
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:
"".解题思路：子字符串问题，可以采用强大的滑动窗口方法解决。首先用map对字符串进行映射，并用两个指针分别指向窗口左边和右边，通过不断的滑动两个指针实现对窗口内字符的操作。
string minWindow(string s, string t) { string res = ""; unordered_map<char,int> map; for(char c:t) map[c]++; int left=0; int right = 0; int distance = INT_MAX; int count = t.size(); int head = 0; while(right < s.size()){ if(map[s[right++]]-- >0) count--; while(count==0){ if(right-left< distance){ head = left; distance = right-head; } if(map[s[left++]]++ ==0) count++; } } return distance==INT_MAX?"":s.substr(head,distance); }
LeetCode-76-Minimum Window Substring
原文：https://www.cnblogs.com/nobodywang/p/10372839.html