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 };