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]
示例 2:
输入:head = [1,2]
输出:[2,1]
示例 3:
输入:head = []
输出:[]
提示:
链表中节点的数目范围是 [0, 5000]
-5000 <= Node.val <= 5000
来源:力扣(LeetCode)
链接:https://leetcode.cn/problems/reverse-linked-list
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//1
public class Solution
{
public ListNode ReverseList(ListNode head)
{
ListNode prev = null, curr = head;
while (curr != null)
{
ListNode next = curr.next;
curr.next = prev;
prev = curr;
curr = next;
}
return prev;
}
}
//2
public class Solution
{
public ListNode ReverseList(ListNode head)
{
if (head == null || head.next == null)
{
return head;
}
ListNode second = head.next;
ListNode newHead = ReverseList(second);
second.next = head;
head.next = null;
return newHead;
}
}