反转链表

题目

牛客网

输入一个链表，反转链表后，输出新链表的表头。

解题思路

1. 三个指针

public ListNode ReverseList(ListNode head) {
    if (head == null || head.next == null) {
        return head;
    }
    ListNode pre = head, cur = head.next, next;
    pre.next = null;
    while (cur != null) {
        next = cur.next;
        cur.next = pre;
        pre = cur;
        cur = next;
    }
    return pre;
}