【leetcode刷题】T121-平衡二叉树

示例 1:
给定二叉树 [3,9,20,null,null,15,7]
    3
   / \
  9  20
    /  \
   15   7
返回 true 。

示例 2:
给定二叉树 [1,2,2,3,3,null,null,4,4]
       1
      / \
     2   2
    / \
   3   3
  / \
 4   4
返回 false 。

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution(object):
    def isBalanced(self, root):
        """
        :type root: TreeNode
        :rtype: bool
        """
        # 左右最大深度之差<=1
        if not root:
            return True
        return self.get_depth(root) != -1

    def get_depth(self, node):
        if not node:
            return 0
        left_depth = self.get_depth(node.left)
        right_depth = self.get_depth(node.right)
        if left_depth < 0 or right_depth < 0 or abs(left_depth - right_depth) > 1:
            return -1
        return max(left_depth, right_depth) + 1

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    bool isBalanced(TreeNode* root) {
        if(!root)
            return true;
        return get_depth(root) != -1;
    }

    int get_depth(TreeNode* node){
        if(!node)
            return 0;
        int left_depth = get_depth(node->left);
        int right_depth = get_depth(node->right);
        if(left_depth < 0 || right_depth < 0 || left_depth - right_depth > 1 || right_depth - left_depth > 1)
            return -1;
        return max(left_depth, right_depth) + 1;
    }
};