19.py

'''
	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.

'''

# 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
        """
        if not head:
        	return None

        ref = head
        while n > 0:
        	ref = ref.next
        	n -= 1

        if ref is None:
        	return head.next
        else:
        	main = head
        	while ref.next:
        		main = main.next
        		ref = ref.next

        	main.next = main.next.next
        	return head