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 <= 0) return null;

ListNode first = head;
ListNode last = head;

for (int count = 1; count <= n; count++;) {
first = first.next;
}

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

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