Balanced Binary Tree

Problem Description

Given a binary tree, determine if it is height-balanced.

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

Example 3:

Input: root = []
Output: true

Constraints:

• The number of nodes in the tree is in the range [0, 5000].
• -104 <= Node.val <= 104

Solution (JavaScript)

/**
 * Definition for a binary tree node.
 * function TreeNode(val, left, right) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.left = (left===undefined ? null : left)
 *     this.right = (right===undefined ? null : right)
 * }
 */
/**
 * @param {TreeNode} root
 * @return {boolean}
 */
var isBalanced = function(root) {
    let balanced = true;
    const iterate = (node) => {
        if (!node) return 0;
        const leftHeight = iterate(node.left);
        const rightHeight = iterate(node.right);
        if (Math.abs(leftHeight - rightHeight) > 1) {
            balanced = false;
        }
        return 1+Math.max(leftHeight, rightHeight);
    }
    iterate(root);
    return balanced;
};