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.

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Example:
Input: nums = [-10,-3,0,5,9]
Output: [0,-3,9,-10,null,5]
Explanation: [0,-10,5,null,-3,null,9] is also accepted:

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 Solution: 

class Solution {
    int[] nums;
    public TreeNode helper(int left, int right){
        if(left > right) return null;
        int p = left + (right - left) / 2;

        TreeNode root = new TreeNode(nums[p]);
        root.left = helper(left, p - 1);
        root.right = helper(p + 1, right);
        return root;
    }
    public TreeNode sortedArrayToBST(int[] nums) {
        this.nums = nums;
        return helper(0, nums.length - 1);
        
    }
    
}

Logic:

• make the scope of int[] nums as a global array
• have a helper function and two variable to find the root 
• and teturn the array
• in the main method pass the arguement to the helper function

Hints:

• make sense of recursion
• draw the stack to understand