Class ListNode

leetcode/19. Remove Nth Node From End of List.py:7–10

   After removing the second node from the end, the linked list becomes 1->2->3->5.
'''
class ListNode(object):
    def __init__(self, x):
        self.val = x
        self.next = None

class Solution(object):
    def removeNthFromEnd(self, head, n):