反转链表（含图解）

题目

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。

示例：

输入：head = [1,2,3,4,5]
输出：[5,4,3,2,1]

图解

题解

ListNode reverse(ListNode head) {
    if (head == null || head.next == null) {
        return head;
    }
    ListNode tail = reverse(head.next);
    head.next.next = head;
    head.next = null;
    return tail;
}

var reverse = function(head) {
    if (head === null || head.next === null) {
        return head;
    }
    var tail = reverse(head.next);
    head.next.next = head;
    head.next = null;
    return tail;
}

def reverse(head: ListNode) -> ListNode:
    if not head or not head.next:
        return head
    tail = reverse(head.next) 
    head.next.next = head 
    head.next = None 
    return tail

func reverse(head *ListNode) *ListNode {
    if head == nil || head.next == nil {
        return head
    }
    tail := reverse(head.next)
    head.next.next = head
    head.next = nil
    return tail
}