Nth to Last Node in List

Problem

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.

Code - Java

/**
 * Definition for ListNode.
 * public class ListNode {
 *   int val;
 *   ListNode next;
 *   ListNode(int val) {
 *     this.val = val;
 *     this.next = 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) {
        ListNode a = head;
        ListNode b = head;
        while (n-- > 0) {
            a = a.next;
        }
        while (a != null) {
            a = a.next;
            b = b.next;
        }
        return b;
    }
}