108. Convert Sorted Array to Binary Search Tree

public class TreeNode
{
    public int val;
    public TreeNode left;
    public TreeNode right;
    public TreeNode(int val = 0, TreeNode left = null, TreeNode right = null)
    {
        this.val = val;
        this.left = left;
        this.right = right;
    }
}

public class Solution
{
    public TreeNode SortedArrayToBST(int[] nums)
    {
        return Build(nums, 0, nums.Length - 1);
    }

    private TreeNode Build(int[] nums, int l, int r)
    {
        if (l > r)
            return null;
        int m = (l + r) / 2;
        return new TreeNode(nums[m], Build(nums, l, m - 1), Build(nums, m + 1, r));
    }
}