Problem URL: Verify preorder serialization of a binary tree

We will split the string with , as delimeter, and pop the last value from it to check whether it's a # or not, if not, we immediately return false. Then we iterate over the values, if the character is not # we append it to the stack and if yes, we pop it from the stack if stack is not empty, if the stack is empty at any point, we will return false again. Finally when the iteration is done, if the stack is empty, we return true else return false.

class Solution:
    def isValidSerialization(self, preorder: str) -> bool:
        preorder = preorder.split(',')
        stack = []

        if preorder.pop() != '#':
            return False

        for c in preorder:
            if c != '#':
                stack.append(c)
            else:
                if not stack:
                    return False
                else:
                    stack.pop()
        return len(stack) == 0

Time Complexity: O(n)
Space Complexity: O(n)