题解 | #最小覆盖子串#

#
# 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
#
# 
# @param S string字符串 
# @param T string字符串 
# @return string字符串
#
class Solution:
    def minWindow(self , S: str, T: str) -> str:
        # write code here
        n,m=len(S),len(T)
        if n<m:
            return ''
        dic,left,right={},0,0
        res,resn='',n+1
        for s in T:
            if s in dic:
                dic[s]-=1
            else:
                dic[s]=-1
        for i in range(n):
            right=i
            if S[i] in dic:
               dic[S[i]]+=1
            while (self.check(dic)):
                if (right-left+1)<resn  :
                    resn=right-left+1
                    res=S[left:right+1]
                if S[left] in dic:
                   dic[S[left]]-=1
                left+=1
        return res    






    def check(self,hash):
        for key in hash:
            if hash[key]<0:
                return False
        return True