task4 (updated)

// O(height) - time complexity,
// O(1) - space complexity.
class Solution {
    public TreeNode trimBST(TreeNode root, int L, int R) {
        if (root == null) {
            return root;
        }
        while (root.val < L || R < root.val) {
            if (root.val < L) {
                root = root.right;
            } else {
                root = root.left;
            }
        }
        {
            TreeNode cur = root;
            while (cur != null) {
                while (cur.left != null && cur.left.val < L) {
                    cur.left = cur.left.right;
                }
                cur = cur.left;
            }
        }
        {
            TreeNode cur = root;
            while (cur != null) {
                while (cur.right != null && R < cur.right.val) {
                    cur.right = cur.right.left;
                }
                cur = cur.right;
            }
        }
        return root;
    }
}