Leetcode 76 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 empty string 

""

.

If there are multiple such windows, you are guaranteed that there will always be only one unique minimum window in S.
找出包含给定串所有字符的最小子串
两个指针向后滑，用map记录出现字符的次数。

class Solution {
public:
string minWindow(string s, string t)
{
int maxlen=INT_MAX;
string result;
unordered_map<char,int> mp,mp2;
int cnt=t.size();
for(int i=0;i<cnt;i++) mp[t[i]]++;
for(int st=0,en=0;en<s.size();en++)
{
if(mp[s[en]]>0 )
{
mp2[s[en]]++;
if(mp2[s[en]]<=mp[s[en]]) cnt--;
}
if(cnt==0)
{
while((mp2[s[st]]==0 || mp2[s[st]]>mp[s[st]]) && st<=en)
{
if(mp2[s[st]]>mp[s[st]]) mp2[s[st]]--;
st++;
}
if(en-st+1<maxlen)
{
maxlen=en-st+1;
result=s.substr(st,en-st+1);
}
cnt++;
mp2[s[st]]--;
st++;
}
}
return result;
}
};