反转链表

package demo;

/*
 * 题目描述
输入一个链表，反转链表后，输出链表的所有元素。
 */
/*
public class ListNode {
    int val;
    ListNode next = null;

    ListNode(int val) {
        this.val = val;
    }
}*/
public class Offer_36 {
    public ListNode ReverseList(ListNode head) {
        ListNode result = null;// 保存结果的ListNode
        ListNode pNode = head;// 暂存结点
        if (head == null)// 若头结点为空，则返回null
            return null;
        ListNode pPrev = null;
        while (pNode != null) {// 结点不为空，则交换结点位置
            ListNode pNext = pNode.next;
            if (pNext == null)
                result = pNode;
            pNode.next = pPrev;
            pPrev = pNode;
            pNode = pNext;
        }
        return result;
    }

    public static void main(String[] args) {
        Offer_36 off = new Offer_36();
        ListNode head = new ListNode(1);
        ListNode head1 = new ListNode(2);
        ListNode head2 = new ListNode(3);
        ListNode head3 = new ListNode(4);
        ListNode head4 = new ListNode(5);
        head.next = head1;
        head1.next = head2;
        head2.next = head3;
        head3.next = head4;
        head4.next = null;
        System.out.println(off.ReverseList(head).next.next.val);
    }
}