LeetCode 110. 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) {
int height = treeHeight(root);
return height == -1 ? false : true;
}

public int treeHeight(TreeNode root) {
if (root == null) return 0;
int leftHeight = treeHeight(root.left);
int rightHeight  = treeHeight(root.right);
if (leftHeight!= -1 && rightHeight != -1 && Math.abs(leftHeight - rightHeight) <= 1)
return Math.max(leftHeight, rightHeight) + 1;
else return -1;
}
}