Nth to Last Node in List

Find the nth to last element of a singly linked list.

The minimum number of nodes in list is n

Example

Given a List 3->2->1->5->null and n = 2, return node whose value is 1.

Solution

"""
Definition of ListNode
class ListNode(object):

    def __init__(self, val, next=None):
        self.val = val
        self.next = next
"""
class Solution:
    """
    @param head: The first node of linked list.
    @param n: An integer.
    @return: Nth to last node of a singly linked list. 
    """
    def nthToLast(self, head, n):
        # write your code here
        fast = head 
        slow = head 
        start = 0
        while fast and n > start:
            fast = fast.next
            start = start + 1
        while fast and slow:
            fast = fast.next
            slow = slow.next
        return slow