[LeetCode] 206. Reverse Linked List_Easy tag: Linked List

Reverse a singly linked list.

Example:

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

Follow up:

A linked list can be reversed either iteratively or recursively. Could you implement both?

很基本的一道换顺序的题目，先建一个pre 指针，设为None，然后将head.next 存到temp node中，然后将head.next 指针指向pre，接着再将pre和head都依次后移一位。

Code：

1) Basic, using temp node

class ListNode:
    def __init__(self, x):
        self.val = x
        self.next = None

class Solution:
    def reverseList(self, head):
        pre = None
        while head:
            temp = head.next
            head.next = pre
            pre = head
            head = temp
        return pre

2) 利用python可以多重赋值

class Solution:
    def reverseList(self, head):
        pre = None
        while head:
            head.next, pre, head = pre, head, head.next
        return pre