1. 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 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 getHeightOrDelta(root) != -1;
    }

    int getHeightOrDelta(TreeNode root){
        if(root == null) return 0;
        int l = getHeightOrDelta(root.left);
        if(l == -1) return -1;
        int r = getHeightOrDelta(root.right);
        if(r == -1) return -1;
        if(Math.abs(l - r) >1 ) return -1;

        return 1 + Math.max(l, r);
    }
}