Introduction

In this blog post, we will explore how to solve the LeetCode problem "331" using AI. LeetCode is a popular platform for preparing for coding interviews, and with the help of AI tools like Chatmagic, we can generate solutions quickly and efficiently - helping you pass the interviews and get the job offer without having to study for months.

Problem Statement

One way to serialize a binary tree is to use preorder traversal. When we encounter a non-null node, we record the node's value. If it is a null node, we record using a sentinel value such as '#'. For example, the above binary tree can be serialized to the string "9,3,4,#,#,1,#,#,2,#,6,#,#", where '#' represents a null node. Given a string of comma-separated values preorder, return true if it is a correct preorder traversal serialization of a binary tree. It is guaranteed that each comma-separated value in the string must be either an integer or a character '#' representing null pointer. You may assume that the input format is always valid. For example, it could never contain two consecutive commas, such as "1,,3". Note: You are not allowed to reconstruct the tree. Example 1: Input: preorder = "9,3,4,#,#,1,#,#,2,#,6,#,#" Output: true Example 2: Input: preorder = "1,#" Output: false Example 3: Input: preorder = "9,#,#,1" Output: false Constraints: 1 <= preorder.length <= 104 preorder consist of integers in the range [0, 100] and '#' separated by commas ','.

Explanation

Here's an efficient solution to the preorder traversal serialization problem:

• Key Idea: Use the concept of slots. Each node consumes one slot but provides two slots for its children (if not null). We iterate through the preorder string, decreasing the available slots for each node. If the number of slots goes negative, it's invalid. If, at the end, the slots are exactly zero, then it is a valid preorder serialization.

• Optimization: The solution can be implemented in O(n) time and O(1) space by iterating through the split preorder string.

• Complexity: O(n) runtime, O(1) storage (excluding the space for the split string).

Code

    class Solution:
    def isValidSerialization(self, preorder: str) -> bool:
        slots = 1
        nodes = preorder.split(',')

        for node in nodes:
            slots -= 1
            if slots < 0:
                return False
            if node != '#':
                slots += 2

        return slots == 0