头条重点

题目

反转一个单链表。

示例:

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

解题思路

1. 三个指针进行反转

public ListNode reverseList(ListNode head) {
    if (head == null) {
        return head;
    }

    if (head.next == null) {
        return head;
    }

    ListNode pre = head;
    ListNode cur = head.next;

    while (cur != null) {
        ListNode next = cur.next;
        cur.next = pre;

        pre = cur;
        cur = next;
    }

    head.next = null;

    return pre;
}