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.
class Solution { public: string minWindow(string s, string t) { int s_size = s.size(); int t_size = t.size(); vector<int> map(256,0); for(int i=0;i<t_size;i++){ map[t[i]]++; } int win_begin=0,win_end=0; int min_win = INT_MAX; int min_win_start = 0; int cnt = t_size; while(win_end < s_size){ if(map[s[win_end]]>0){ cnt--; } map[s[win_end]]--; win_end++; while(cnt==0){ if(win_end-win_begin < min_win){ min_win = win_end-win_begin; min_win_start = win_begin; } if(map[s[win_begin]]==0){ cnt++; } map[s[win_begin++]]++; } } return min_win == INT_MAX ? "":s.substr(min_win_start,min_win); } };
[string]Minimum Window Substring
原文：http://www.cnblogs.com/zengzy/p/5043354.html