[leetcode] 76 Minimum Window Substring

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).

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.

代码：

string minWindow(string S, string T) {  //C++
int size_s = S.size();
int size_t = T.size();
if(size_t == 0||size_s==0||size_s<size_t)
return "";

string result;
map<char,int> dic;
map<char,int> window;
int validNum = 0,min = INT_MAX;

for(int i=0; i<size_t; i++)
dic[T[i]]++;
for(int fast=0,slow=0; fast<size_s;fast++){
char ch = S[fast];
if(dic.count(ch)!=0){
window[ch]++;
if(window[ch] <= dic[ch])
validNum++;
}
if(validNum == size_t){
while(dic.count(S[slow])==0||dic[S[slow]]<window[S[slow]]){
if(window.count(S[slow])!=0)
window[S[slow]]--;
slow++;
}
if(fast-slow+1 < min){
min = fast-slow+1;
result = S.substr(slow,min);
}
}

}
return result;
}