Leetcode | 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 depth of the two subtrees of every node never differ by more than 1.

判断左右子树的高度相差是否大于1. 

树的高度取决于左右子树的高度的最大值。

 1 /**

 2  * Definition for binary tree

 3  * struct TreeNode {

 4  *     int val;

 5  *     TreeNode *left;

 6  *     TreeNode *right;

 7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}

 8  * };

 9  */

10 class Solution {

11 public:

12     bool isBalanced(TreeNode *root) {

13         return getLayer(root, 1) != -1;

14     }

15     

16     int getLayer(TreeNode *root, int layer) {

17         if (root == NULL) return layer;

18         int l = getLayer(root->left, layer + 1);

19         if (l == -1) return -1;

20         int r = getLayer(root->right, layer + 1);

21         if (r == -1) return -1;

22         if (abs(l - r) > 1) return -1;

23         return l > r ? l : r;

24     }

25 };

 3-rd try:

 1 class Solution {

 2 public:

 3     bool isBalanced(TreeNode *root) {

 4        int height = 0;

 5        return recurse(root, height);

 6     }

 7     

 8     bool recurse(TreeNode *root, int &height) {

 9         if (root == NULL) return true;

10         int lheight = 0, rheight = 0;

11         if (!recurse(root->left, lheight) || !recurse(root->right, rheight)) return false;

12         height = 1 + (lheight > rheight ? lheight : rheight);

13         return abs(lheight - rheight) <= 1;

14     }

15 };