```
class Solution:
def minWindow(self, s, t):
"""
:type s: str
:type t: str
:rtype: str
"""
arr = [0] * 128
for c in t:
arr[ord(c) - ord('A')] += 1
i = j = 0
res = ''
for j in range(len(s)):
arr[ord(s[j]) - ord('A')] -= 1
while max(arr) <= 0:
res = s[i:j+1] if res == '' or j+1 - i < len(res) else res
arr[ord(s[i]) - ord('A')] += 1
i += 1
return res
```