Leetcode19 Remove Nth Node From End of List

class Solution:    # @param {ListNode} head    # @param {integer} n    # @return {ListNode}    def removeNthFromEnd(self, head, n):        dummy=ListNode(0); dummy.next=head        p1=p2=dummy        for i in range(n): p1 = p1.next        while p1.next:            p1 = p1.next; p2 = p2.next        p2.next = p2.next.next        return dummy.next