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 left and right subtrees of every node differ in height by no more than 1.

Java Solution:

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Result {
    boolean val;
    Result() {
        this.val = true;
    }
    public void setValue(boolean val) {
        this.val = val;
    }
    public boolean getValue() {
        return val;
    }
}
class Solution {
    public boolean isBalanced(TreeNode root) {
        Result isBalanced = new Result();
        getHeight(root, isBalanced);
        return isBalanced.getValue();
    }
    
    private int getHeight(TreeNode node, Result isBalanced) {
        if (node == null) return 0;
        int leftHeight = getHeight(node.left, isBalanced);
        int rightHeight = getHeight(node.right, isBalanced);
        if (Math.abs(leftHeight - rightHeight) > 1) {
            isBalanced.setValue(false);
        }
        return Math.max(leftHeight, rightHeight) + 1;
    }
}

Essentially, trying to “hack” the pass-by-reference C++ has into the Java solution. But it solves the problem in one pass.