Convert Sorted Array to Binary Search Tree

Question: Given an array where elements are sorted in ascending order, convert it to a height balanced BST.

For this problem, a height-balanced binary tree is defined as a binary tree in which the depth of the two subtrees of every node never differ by more than 1.

You may view the full question here.

Approach 1: There isn’t a unique solution for this question. Here’s one approach that uses recursion —

//Approach 1:
//Runtime: 0ms
//Memory usage: 35.2MB
/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public TreeNode sortedArrayToBST(int[] nums) {
        return sort(nums, 0, nums.length-1);
    }
    
    private TreeNode sort(int[] nums, int start, int end){
        if(start==end){
            return new TreeNode(nums[start]);
        } else if(start<end){
            int mid = (start+end)/2;
            TreeNode node = new TreeNode(nums[mid]);
            node.left = sort(nums, start, mid-1);
            node.right = sort(nums, mid+1, end);
            return node;
        }
        return null;
    }
}

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