def test(head_list, n, ans_list):
head = ListNode.fromList(head_list)
ans = ListNode.fromList(ans_list)
s = Solution()
r = s.removeNthFromEnd(head, n)
if r != ans:
print('not correct', head_list, n, r, ans)
def test(head_list, k, ans_list):
head = ListNode.fromList(head_list)
ans = ListNode.fromList(ans_list)
s = Solution()
r = s.reverseKGroup(head, k)
if r != ans:
print('not correct', head_list, k, r, ans)
def test(head_list, ans_list):
head = ListNode.fromList(head_list)
ans = ListNode.fromList(ans_list)
s = Solution()
r = s.swapPairs(head)
if r != ans:
print('not correct', head_list, r, ans)