【LeetCode】Convert Sorted Array to Binary Search Tree

/**
* 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 *GetNode(vector <int> &num, int left, int right)
{
if(left <= right)//not while!
{
int mid = (right + left) / 2;
TreeNode *node = new TreeNode(num[mid]);
node->left = GetNode(num, left, mid-1);
node->right = GetNode(num, mid+1, right);
return node;
}
return NULL;//necessary,otherwise runtime error occurs
}

TreeNode *sortedArrayToBST(vector<int> &num)
{
if(num.size() == 0) return NULL;

return GetNode(num, 0, num.size()-1);
}
};