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.

　　

 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 * BST(vector<int> num, int left, int right)

13     {

14         //if(left > right ) return NULL;

15 

16         int mid = (right +left)/2;

17         

18         TreeNode *p = new TreeNode(num[mid]);

19     

20         p->left  =  left <=  mid-1 ? BST(num, left, mid-1) : NULL ;

21         p->right = mid+1 <= right  ? BST(num, mid+1, right): NULL ;

22       

23        return p;

24     }

25     TreeNode *sortedArrayToBST(vector<int> &num) {

26         // Start typing your C/C++ solution below

27         // DO NOT write int main() function

28         int size = num.size();

29         TreeNode *myTree = NULL;

30         

31         if(0 == size )

32              return myTree;

33         

34         myTree = BST(num, 0, size-1);

35         

36         return myTree;

37         

38         

39     }

40 };