[LeetCode]Convert Sorted Array to Binary Search Tree

struct TreeNode {
	int val;
	TreeNode *left;
	TreeNode *right;
	TreeNode(int x) : val(x), left(NULL), right(NULL) {}
};

class Solution {
public:
	TreeNode* Convert2BST(vector<int>& num, int start, int end)
	{
		if(start > end)
			return NULL;
		int mid = (start+end)/2;
		TreeNode* pNode = new TreeNode(num[mid]);
		pNode->left = Convert2BST(num, start, mid-1);
		pNode->right = Convert2BST(num, mid+1, end);
		return pNode;
	}
    TreeNode *sortedArrayToBST(vector<int> &num) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        return Convert2BST(num, 0, num.size()-1);
    }
};

second time

/**
 * 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* sortedArrayToBSTUtil(vector<int>& num, int start, int end)
    {
        if(start > end) return NULL;
        int mid = start+(end-start)/2;
        TreeNode* root = new TreeNode(num[mid]);
        root->left = sortedArrayToBSTUtil(num, start, mid-1);
        root->right = sortedArrayToBSTUtil(num, mid+1, end);
        return root;
    }
    TreeNode *sortedArrayToBST(vector<int> &num) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        return sortedArrayToBSTUtil(num, 0, num.size()-1);
    }
};