108. Convert Sorted Array to Binary Search Tree

Given an integer array nums where the elements are sorted in ascending order, convert it to a height-balanced binary search tree.

A height-balanced binary tree is a binary tree in which the depth of the two subtrees of every node never differs by more than one.

/**
 * 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 {
    TreeNode* helper(vector<int>& A, int l, int r) {
        if(l > r) return nullptr;
        int m = l + (r - l) / 2;
        TreeNode* node = new TreeNode(A[m]);
        node->left = helper(A,l,m-1);
        node->right = helper(A,m+1,r);
        
        return node;
    }
public:
    TreeNode* sortedArrayToBST(vector<int>& nums) {
        return helper(nums,0,nums.size()-1);
    }
};