题解 | #反转链表#

/*
public class ListNode {
    int val;
    ListNode next = null;

    ListNode(int val) {
        this.val = val;
    }
}*/
public class Solution {
    public ListNode ReverseList(ListNode head) {
        if (head == null || head.next == null) {
            return head;
        }

        ListNode pre = null;
        ListNode cur = head;
        ListNode tmp = null;

        while (cur != null){
            //先保存tmp
            tmp = cur.next;

            //反转链表
            cur.next = pre;

            //整体后移
            pre = cur;
            cur = tmp;
        }

        //cur 此时为null，输出pre
        return pre;
    }
}