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.

　　

 /**
  * Definition for binary tree
  * struct TreeNode {
  *     int val;
  *     TreeNode *left;
  *     TreeNode *right;
  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
  * };
  */
 class Solution {
 public:
     TreeNode * BST(vector<int> num, int left, int right)
     {
         //if(left > right ) return NULL;

         int mid = (right +left)/;

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

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

        return p;
     }
     TreeNode *sortedArrayToBST(vector<int> &num) {
         // Start typing your C/C++ solution below
         // DO NOT write int main() function
         int size = num.size();
         TreeNode *myTree = NULL;

         if( == size )
              return myTree;

         myTree = BST(num, , size-);

         return myTree;

     }
 };