'''
Given a linked list, remove the nth node from the end of list and return its head.
For 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.
'''
class ListNode(object):
def __init__(self, x):
self.val = x
self.next = None
class Solution(object):
def removeNthFromEnd(self, head, n):
if not head and n <= 0:
return None
pNode = ListNode(0)
pNode.next = head
first, second = pNode, pNode
for i in range(n):
if first.next:
first = first.next
else:
return None
while first.next:
first = first.next
second = second.next
second.next = second.next.next
return pNode.next
