108. Convert Sorted Array to Binary Search Tree

time: O(n), must visit all nums element

space: O(n), must build all nums element, O(logn) for recursion stack, because use binary search idea

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

        node.left = helper(nums, left, mid - 1);
        node.right = helper(nums, mid + 1, right);
        return node;
    }
}