Balanced Binary Tree

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

For this problem, a height-balanced binary tree is defined as:

a binary tree in which the depth of the two subtrees of_every_node never differ by more than 1.

Example 1:

Given the following tree[3,9,20,null,null,15,7]:

    3
   / \
  9  20
    /  \
   15   7

Return true.

Example 2:

Given the following tree[1,2,2,3,3,null,null,4,4]:

       1
      / \
     2   2
    / \
   3   3
  / \
 4   4

Return false.

Solution

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    private boolean balanced = true;

    public boolean isBalanced(TreeNode root) {
        depth(root);
        return balanced;
    }

    private int depth(TreeNode node) {
        if (node == null) return 0;
        int left = depth(node.left);
        int right = depth(node.right);
        if (Math.abs(left - right) > 1) {
            balanced = false;
        }
        return Math.max(left, right) + 1;
    }
}