110. determine whether a tree is a balanced binary tree

Topic narrative:

Given a binary tree to determine whether it is a highly balanced binary tree.
In this problem, a well-balanced binary tree is defined as:
the absolute value of the difference between the height of the left and right subtrees a binary tree each node is not more than 1.

Ideas:

• Requires every node is a root node of a subtree are balanced
  above problem is equivalent to the following two conditions:
  1. For any one of the root node, its left subtree balance, the balance is also right subtree
  2. about sub absolute difference is smaller than the height of the tree 2

Code:

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public boolean isBalanced(TreeNode root) {
        if(root == null) return true;
        if(root.left == null && root.right == null) return true;
        return isBalanced(root.left)&&isBalanced(root.right)&&Math.abs(height(root.left)-height(root.right))<=1;
    }
    //求一棵树的高度
    public int height(TreeNode root){
        if(root == null) return 0;
        return Math.max(height(root.left),height(root.right)) + 1;
    }
}