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.

分析：

要找到nth to last element，我们需要两个指针，第一个指针先走n步，然后两个指针同时走，知道第一个指针为null.

 public class Solution {
     /**
      * @param head: The first node of linked list.
      * @param n: An integer.
      * @return: Nth to last node of a singly linked list.
      */
     ListNode nthToLast(ListNode head, int n) {
         if (head == null || n <= ) return null;

         ListNode first = head;
         ListNode last = head;

         for (int count = ; count <= n; count++;) {
             first = first.next;
         }

         while(first != null) {
             first = first.next;
             last = last.next;
         }
         return last;
     }
 }

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