108. Convert Sorted Array to Binary Search Tree

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.

Example:

Given the sorted array: [-10,-3,0,5,9],

One possible answer is: [0,-3,9,-10,null,5], which represents the following height balanced BST:

      0
     / \
   -3   9
   /   /
 -10  5

Solution:

class Solution {
    public TreeNode sortedArrayToBST(int[] nums) {
        return sorted(nums,0,nums.length-1);
    }
    
    public TreeNode sorted(int[] nums, int i, int j){
        if(i>j) return null;
        int mid = (i+j)/2;
        TreeNode head = new TreeNode(nums[mid]);
        head.left = sorted(nums,i,mid-1);
        head.right = sorted(nums,mid+1,j);
        return head;
    }
}