206. Reverse Linked List

不用多说，考察链表的基本功，定义一个prev，定义一个cur，其实同swap(a,b)相似，先save，再交换，再更新，最后返回prev

/** * Definition for singly-linked list. * public class ListNode { *     int val; *     ListNode next; *     ListNode(int x) { val = x; } * } */class Solution {    public ListNode reverseList(ListNode head) {        ListNode prev = null;        ListNode cur = head;        while (cur != null) {            ListNode tmp = cur.next;            cur.next = prev;            prev = cur;            cur = tmp;        }        return prev;    }}