Same Tree

Problem

Given the roots of two binary trees p and q, write a function to check if they are the same or not.

Examples

The brute-force approach

Serialize both trees to strings (level-order) and compare the strings.

def serialize(node):
    if not node:
        return 'null'
    return f'{node.val},{serialize(node.left)},{serialize(node.right)}'

return serialize(p) == serialize(q)

Serializing is O(n) time and O(n) space, and it works. But the direct recursive comparison is also O(n) and more natural, and it short-circuits as soon as it finds a mismatch, without building any strings.

Spotting the pattern

This is a Tree Traversal problem. The key question to ask yourself:

Can I recursively compare corresponding nodes in both trees and short-circuit on any mismatch?

Answering that is where it clicks, and it's exactly what the guided walkthrough below builds with you: the pattern reasoning, a progressive hint ladder that never spoils the answer, a row-by-row dry run, the optimized solution, and an in-browser editor to run your code against real test cases.