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