Leetcode 19. Remove Nth Node From End of List（python）

# Definition for singly-linked list.
# class ListNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution(object):
    def removeNthFromEnd(self, head, n):
        """
        :type head: ListNode
        :type n: int
        :rtype: ListNode
        """
        left=right=head
        for i in range(n):
            right=right.next
        if right is None:   return head.next    #special
        while right.next is not None:
            right=right.next
            left=left.next
            
        left.next=left.next.next
        return head