leetcode76

 class Solution:
     def minWindow(self, s: str, t: str) -> str:
         n = len(s)
         if n==0:
             return ""
         if len(t)==0:
             return s
         #if s == t:
         #    return s
         dic = {}
         dic2= {}
         for i in range(len(t)):
             dic.update({t[i]:0})
             if t[i] in dic2.keys():
                 dic2.update({t[i]:dic2[t[i]]+1})
             else:
                 dic2.update({t[i]:1})
         #dicount = len(t)
         i = 0
         j = 0
         minstr = ""
         minwidth = n
         while i <=j and j<n :
             #j++
             if s[j] in t:
                 dic.update({s[j]:dic[s[j]]+1})
                 valid = True
                 for k in dic.keys():
                     if dic[k]<dic2[k]:
                         valid = False
                         break
                 if valid:
                     #valid
                     curlen = j-i+1
                     if curlen<=minwidth:
                         minwidth = curlen
                         minstr = s[i:j+1]
                     #i++
                     while i<=j:
                         if s[i] not in dic.keys():
                             i += 1
                         else:
                             if dic[s[i]]>dic2[s[i]]:
                                 dic.update({s[i]:dic[s[i]]-1})
                                 i += 1
                             else:
                                 curlen = j-i+1
                                 if curlen <= minwidth:
                                     minwidth = curlen
                                     minstr = s[i:j+1]
                                 break
                 #else:
                     #invalid

             j += 1

         return minstr