# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None
#
# 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
#
# 
# @param head ListNode类 
# @param n int整型 
# @return ListNode类
#
class Solution:
    def removeNthFromEnd(self, head, n):    
        #左右指针指向头结点
        slow = fast = head
        #fast先走n步
        while n > 0 and fast:
            fast = fast.next
            n = n - 1
            
        if not fast:
            return head.next
        
        while fast.next:
            slow = slow.next
            fast = fast.next
        slow.next = slow.next.next
        return head