Python实现"反转链表"的两种方法

反转一条单链表

Example:

Input: 1->2->3->4->5->NULL
Output: 5->4->3->2->1->NULL

进阶：

请用迭代和递归的方法分别实现反转单链表

1：迭代方法，通过声明一个头指针进行节点与节点之间的链接

def reverseList(self, head):
        """
        :type head: ListNode
        :rtype: ListNode
        """
        headNode = ListNode(0)
        while head is not None:
            temp = head.next
            head.next = headNode.next
            headNode.next = head
            head = temp
        return headNode.next

2：递归方法

class Solution(object):
    def reverseList(self, head):
        """
        :type head: ListNode
        :rtype: ListNode
        """
        if not head:
            return None
        headAndCur = self.reverseList1(head)
        return headAndCur[0].next
        
        
    def reverseList1(self, head):   #由于递归时，为了节省时间开支，需要传递头指针和当前节点，所以另声明一个函数
        if not head.next:
            headNode = ListNode(0)    #头节点
            curNode = ListNode(head.val)   #当前节点
            headNode.next = curNode
            return [headNode, curNode]
        tempList = self.reverseList1(head.next)  
        tempList[1].next = ListNode(head.val)
        tempList[1] = tempList[1].next
        return tempList

参考他人的代码：

def reverseList(self, head):
        """
        :type head: ListNode
        :rtype: ListNode
        """
        if not head:
            return None
        if not head.next:
            return head
        headNode = self.reverseList(head.next)
        head.next.next = head
        head.next = None
        return headNode

算法题来自：https://leetcode-cn.com/problems/reverse-linked-list/description/