[LeetCode] Convert Sorted Array to Binary Search Tree

Given an array where elements are sorted in ascending order, convert it to a height balanced BST.

二分递归转换

 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     TreeNode *createTree(vector<int> &num, int left, int right)
13     {
14         if (left > right)
15             return NULL;
16             
17         int mid = (left + right) / 2;
18         
19         TreeNode *leftNode = createTree(num, left, mid - 1);
20         TreeNode *rightNode = createTree(num, mid + 1, right);
21         
22         TreeNode *node = new TreeNode(num[mid]);
23         
24         node->left = leftNode;
25         node->right = rightNode;
26         
27         return node;
28     }
29     
30     TreeNode *sortedArrayToBST(vector<int> &num) {
31         // Start typing your C/C++ solution below
32         // DO NOT write int main() function
33         return createTree(num, 0, num.size() - 1);    
34     }
35 };