Balanced Binary Tree

/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
public class Solution {
public boolean isBalanced(TreeNode root) {
return maxDepth(root) != -1;
}
private int maxDepth (TreeNode node) {
if (node == null) {
return 0;
}
int left = maxDepth(node.left);
int right = maxDepth(node.right);
if (left == -1 || right == -1 || Math.abs(left - right) > 1) {
return -1;
}
return Math.max(left, right) + 1;
}
}