数组练习（四）：反转链表

定义一个函数，输入一个链表的头节点，反转该链表并输出反转后链表的头节点。

示例:

输入: 1->2->3->4->5->NULL
输出: 5->4->3->2->1->NULL

　　

解题思路：

考虑遍历链表，并在访问各节点时修改 next 引用指向

package Algriothm;

public class Solution2 {

    public static void main(String[] args) {
        ListNode head1 = new ListNode(1);
        ListNode head2 = new ListNode(2);
        ListNode head3 = new ListNode(3);
        ListNode head4 = new ListNode(4);
        ListNode head5 = new ListNode(5);
        head1.next = head2;
        head2.next = head3;
        head3.next = head4;
        head4.next = head5;
        System.out.println(reverseList(head1));
    }
    public static ListNode reverseList(ListNode head) {
        ListNode cur = head, pre = null;
        while (cur != null) {
            ListNode tmp = cur.next;
            cur.next = pre;
            pre = cur;
            cur = tmp;
        }
        return pre;
    }
}