Verify Preorder Serialization of a Binary Tree (medium)

Grokking Tree Coding Patterns for Interviews

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Perhaps a cleaner and more readable approach, though it uses O(N) space.

Dakshesh Jain

Mar 15, 2025

class Solution:
    def isValidSerialization(self, preorder: str) -> bool:
        nodes = preorder.split(',')
        available_slots = 1 # for root node

        for node in nodes:
            # since node is processed 
            available_slots -= 1

            # negative slots can't be possible
            if available_slots < 0:
                return False

            # since this is not a null node it will create 2 slots
            if node != "#":
                available_slots += 2
        
        # finally checking if all slots are exactly filled
        return available_slots == 0

Perhaps a cleaner and more readable approach, though it uses O(N) space.

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