leetcode 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.

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    
        private int heightOfTree(TreeNode root) {
        int height;
        if (root == null) {
            return -1;
        }
        
        int hleft=heightOfTree(root.left);
        int rlegt=heightOfTree(root.right);
        height=1+Math.max(hleft, rlegt);
        return height;
    }
    
    public boolean isBalanced(TreeNode root) {
        if (root == null) {
            return true;
        }
        int height=heightOfTree(root.left)-heightOfTree(root.right);
        if (height>1 || height<-1) {
            return false;
        }
        if (!isBalanced(root.left)) {
            return false;
        }
        if (!isBalanced(root.right)) {
            return false;
        }
        return true;
        
    }
}