019-remove-nth-node-from-end-of-list.py

"""
Problem Link: https://leetcode.com/problems/remove-nth-node-from-end-of-list/

Given a linked list, remove the n-th node from the end of list and return its head.

Example:
Given linked list: 1->2->3->4->5, and n = 2.
After removing the second node from the end, the linked list becomes 1->2->3->5.

Note:
Given n will always be valid.

Follow up:
Could you do this in one pass?
"""
# 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
        """
        p1,p2 = head,head
        if not head:
            return head
        for i in range(n):
            p1 = p1.next
        if not p1:
            return p2.next
        while p1.next != None:
            p1 = p1.next
            p2 = p2.next
        p2.next = p2.next.next
        return head