1 class Solution {
 2 public:
 3     string minWindow(string s, string t) {
 4         int m = s.length(), n = t.length();
 5         if (!m || !n) return "";
 6         int times[128] = {0};
 7         bool exist[128] = {false};
 8         for (int i = 0; i < n; i++) {
 9             times[t[i]]++;
10             exist[t[i]] = true;
11         }
12         int l = 0, r = -1, idx = 0, len = INT_MAX;
13         while (l < m && r < m) {
14             if (n) {
15                 times[s[++r]]--;
16                 if (exist[s[r]] && times[s[r]] >= 0) n--;
17             }
18             else {
19                 if (len > r - l + 1) {
20                     len = r - l + 1;
21                     idx = l;
22                 }
23                 times[s[l]]++;
24                 if (exist[s[l]] && times[s[l]] > 0) n++;
25                 l++;
26             }
27         }
28         return len == INT_MAX ? "" : s.substr(idx, len);
29     }
30 };