331

class Solution:
    def isValidSerialization(self, preorder: str) -> bool:
        seq = preorder.split(',')
        # For binary tree.. #nodes = #edges + 1
        edges = 1
        for p in seq:
            edges = edges-1
            if edges < 0:
                return False
            if p != '#':
                edges = edges+2

        return edges == 0