[Leetcode] Convert Sorted Array to Binary Search Tree

 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     void buildTree(TreeNode *&root, vector<int> &num, int l, int h) {
13         if (l <= h) {
14             int mid = (l + h) / 2;
15             root = new TreeNode(num[mid]);
16             buildTree(root->left, num, l, mid - 1);
17             buildTree(root->right, num, mid + 1, h);
18         }
19     }
20     
21     TreeNode *sortedArrayToBST(vector<int> &num) {
22         if (num.size() < 1) {
23             return NULL;
24         }
25         TreeNode *root;
26         buildTree(root, num, 0, num.size() - 1);
27         return root;
28     }
29 };