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.

the tree is only balanced if:

1. The left and right subtrees' heights differ by at most one, AND
2. The left subtree is balanced, AND
3. The right subtree is balanced

so tree like this is also balanced:

                  o

                /

              o      o

            /      /  

          o      o       o

               /

             o

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public boolean isBalanced(TreeNode root) {
        // IMPORTANT: Please reset any member data you declared, as
        // the same Solution instance will be reused for each test case.
        return (check(root) != -1);
    }
    public int check(TreeNode node){
        if(node == null) return 0;
        else{
            int left = check(node.left);
            if(left == -1) return -1;
            int right = check(node.right);
            if(right == -1) return -1;
            if(Math.abs(left - right) < 2) return (left > right ? left : right) + 1;
            else return -1;
        }
    }
}