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 left and right subtrees of every node differ in height by no more than 1.

Example 1:

Given the following tree [3,9,20,null,null,15,7]:

    3
   / \
  9  20
    /  \
   15   7

Return true. Example 2:

Given the following tree [1,2,2,3,3,null,null,4,4]:

       1
      / \
     2   2
    / \
   3   3
  / \
 4   4

Return false.

class Solution {
    public int height(TreeNode root) {
        if (root == null)
            return 0;
        int leftHeight = height(root.left);
        if (leftHeight == -1)
            return -1;
        int rightHeight = height(root.right);
        if (rightHeight == -1)
            return -1;
        if (Math.abs(leftHeight - rightHeight) > 1)
            return -1;
        return Math.max(leftHeight, rightHeight) + 1;
    }

    public boolean isBalanced(TreeNode root) {
        return height(root) == -1 ? false : true;
    }
}