19. 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:
    def __init__(self, x):
        self.val = x
        self.next = None

class Solution:
    def removeNthFromEnd(self, head, n):
        """
        :type head: ListNode
        :type n: int
        :rtype: ListNode
        """
        if head is None or head.next is None:
            return None
        slow = fast = head
        for i in range(n):
            fast = fast.next
        if fast is None:
            head = head.next
            return head
        while fast.next:
            fast = fast.next
            slow = slow.next
        slow.next = slow.next.next
        return head