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

# -*- coding:utf-8 -*-


# 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
        """
        dummy = ListNode(0)
        dummy.next = head
        fast = slow = dummy
        
        while n:
            fast = fast.next
            n = n-1
        
        while fast.next:
            fast = fast.next
            slow = slow.next
        slow.next = slow.next.next
        return dummy.next