Balanced Binary Tree

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Problem

Given the root of a binary tree, determine whether it is height-balanced — for every node, the heights of its left and right subtrees differ by at most 1.

Examples

Example 1

Input:root = [3,9,20,null,null,15,7]

Output:true

Example 2

Input:root = [1,2,2,3,3,null,null,4,4]

Output:false

Constraints

0 <= number of nodes <= 5000

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How to approach it: the Trees pattern

A tree is a hierarchical structure where each node has at most a fixed number of children (two, for binary trees). Almost every tree problem reduces to a traversal — decide what order you visit nodes in, and what you do at each one.

Look for this pattern when

The problem is naturally recursive: "the answer for this tree depends on the answer for its subtrees."
You need level-by-level information (BFS) versus depth-first structural information (DFS).

Read the full Trees guide →

Video walkthroughs

Original problem on LeetCode ↗