class Solution: def isValidSerialization(self, preorder): stack = [] for elem in preorder.split(","): stack.append(elem) while len(stack) > 2 and stack[-2:] == ["#"]*2 and stack[-3] != "#": stack.pop(-3) stack.pop(-2) return stack == ["#"]
class Solution: def isValidSerialization(self, preorder): stack = [] for elem in preorder.split(","): stack.append(elem) while len(stack) > 2 and stack[-2:] == ["#"]*2 and stack[-3] != "#": stack.pop(-3) stack.pop(-2) return stack == ["#"]