108. Convert Sorted Array to Binary Search Tree

class Solution {
    private int[] nums;

    public TreeNode sortedArrayToBST(int[] nums) {
        this.nums = nums;
        return dfs(0, nums.length - 1);
    }

    private TreeNode dfs(int l, int r) {
        if (l > r) {
            return null;
        }
        int mid = (l + r) >> 1;
        TreeNode left = dfs(l, mid - 1);
        TreeNode right = dfs(mid + 1, r);
        return new TreeNode(nums[mid], left, right);
    }
}