Convert Sorted Array to Binary Search Tree

 1 class Solution {
 2 public:
 3     TreeNode *sortedArrayToBST( vector<int> &num ) {
 4         return ConvertSubArray( num, 0, (int)num.size()-1 );
 5     }
 6 private:
 7     TreeNode *ConvertSubArray( vector<int> &num, int start, int end ) {
 8         if( start > end ) { return 0; }
 9         int middle = ( start + end ) / 2;
10         TreeNode *treeNode = new TreeNode( num[middle] );
11         treeNode->left = ConvertSubArray( num, start, middle-1 );
12         treeNode->right = ConvertSubArray( num, middle+1, end );
13         return treeNode;
14     }
15 };