LeetCode-Balanced Binary Tree

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Description：
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.

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.

题意：判断一颗二叉树是否为平衡二叉树；

解法：平衡二叉树的定义为，树中的每一个节点必须满足其左右子树的深度差不大于1；根据此定义，我们只需要递归的判断树中的每一个节点即可；

Java

/**
 * 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) {
        return deepth(root) != -1;
    }
    
    private int deepth(TreeNode root) {
        if (root == null) {
            return 0;
        }
        int left = deepth(root.left);
        int right = deepth(root.right);
        if (left == -1 || right == -1 || Math.abs(left - right) > 1) {
            return -1;
        }
        
        return Math.max(left, right) + 1;
    }
}