110. Balanced Binary Tree

这道题重点是要明白平衡二叉树的定义。题目中给出的定义就是左右子树的高度不超过一。 参考了以下链接：

https://blog.csdn.net/DERRANTCM/article/details/47414041

代码如下：

/**
 * 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;
        }
        
        int left = depth(root.left);
        int right = depth(root.right);
        
        if( Math.abs(left - right ) > 1){
            return false;
        }else{
            return isBalanced(root.left) && isBalanced(root.right);
        }
    }
    
    private int depth(TreeNode n){
        if( n == null){
            return 0;
        }
        
        if (n.left == null && n.right == null) {
            return 1;
        } else {
            int left = depth(n.left);
            int right = depth(n.right);
            return 1 + (left > right ? left : right);
        }
    }
    

}

END