LintCode 35. 翻转链表

import org.junit.Test;

public class Reverse {
    /**
     * @param head: n
     * @return: The new head of reversed linked list.
     * 
     *
    35. 翻转链表
    翻转一个链表

    样例
    给出一个链表1->2->3->null，这个翻转后的链表为3->2->1->null

    挑战
    在原地一次翻转完成
     */
    public ListNode reverse(ListNode head) {
        // write your code here
        ListNode listNodePrev = null;
        ListNode listNodeNext = null;

        while (head != null) {
            listNodeNext = head;
            head = head.next;
            listNodeNext.next = listNodePrev;
            listNodePrev = listNodeNext;
        }
        return listNodeNext;
    }

    @Test
    public void testReverse() {
        ListNode head = new ListNode(1);
        head.next = new ListNode(2);
        head.next.next = new ListNode(3);

        showList(head);

        if (head == null) {
            System.out.println("head == null");
        }
        showList(reverse(head));

    }

    public void showList(ListNode head) {
        while (head != null) {
            System.out.println(head.val);
            head = head.next;
        }
    }
}