leetcode1003

 class Solution:
     def isValid(self, S: str) -> bool:
         n = len(S)
         if n % 3 != 0:
             return False
         while n!=0:
             i = S.find('abc')
             if i == -1:
                 return False
             else:
                 S = S[0:i] + S[i+3:]
                 n = len(S)
         return True