[LeetCode] #206 反转链表

[LeetCode] #206 反转链表

给你单链表的头节点

head

，请你反转链表，并返回反转后的链表。

输入：head = [1,2,3,4,5]

输出：[5,4,3,2,1]

迭代，需要一个临时变量先保存下一个节点

class Solution {
    public ListNode reverseList(ListNode head) {
        ListNode p1 = null,p2 = head;
        while(p2 != null){
            ListNode temp = p2.next;
            p2.next = p1;
            p1 = p2;
            p2 = temp;
        }
        return p1;
    }
}      

class Solution {
    public ListNode reverseList(ListNode head) {
        if(head == null || head.next == null) return head;
        ListNode newListNode = reverseList(head.next);
        head.next.next = head;
        head.next = null;
        return newListNode;
    }
}