Convert Sorted Array to Binary Search Tree.cpp

// https://leetcode.com/problems/convert-sorted-array-to-binary-search-tree/

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