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.

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/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
    
public:
    TreeNode* foo(vector<int>& nums, int left, int right)
    {
        if (left > right)
            return NULL;
            
        int mid = (left+right)/2;
        TreeNode *node = new TreeNode(nums[mid]);
        node->left  = foo(nums, left, mid-1);
        node->right = foo(nums, mid+1, right);
        
        return node;
        
    }
    
public:
    TreeNode* sortedArrayToBST(vector<int>& nums) {
        
        return foo(nums, 0, nums.size()-1);
    }
};