1 class Solution: 2     def isValid(self, S: str) -> bool: 3         n = len(S) 4         if n % 3 != 0: 5             return False 6         while n!=0: 7             i = S.find('abc') 8             if i == -1: 9                 return False10             else:11                 S = S[0:i] + S[i+3:]12                 n = len(S)13         return True