/**
 * 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 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 helper(root) >= 0;
    }
    
    //get the height of n
    private int helper(TreeNode n) {
        if(n == null) return 0;
        int hleft = helper(n.left);
        int hright = helper(n.right);
        if(hleft == -1 || hright == -1 || Math.abs(hleft - hright) > 1) return -1;
        return Math.max(hleft, hright)+1;
    }
}

Create 110.java