[LeetCode]24. 两两交换链表中的节点（Swap Nodes in Pairs）

题目描述

给定一个链表，两两交换其中相邻的节点，并返回交换后的链表。

你不能只是单纯的改变节点内部的值，而是需要实际的进行节点交换。

示例:

给定 1->2->3->4, 你应该返回 2->1->4->3.

解题思路

略。

代码

Python 3.6

解法一：递归

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution:
    def swapPairs(self, head: ListNode) -> ListNode:
        if head is None or head.next is None:
            return head
        head_next = head.next
        head.next = self.swapPairs(head_next.next)
        head_next.next = head
        return head_next

执行用时 : 48 ms
内存消耗 : 13.9 MB

解法二：循环

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution:
    def swapPairs(self, head: ListNode) -> ListNode:
        dummy = ListNode(-1)
        dummy.next = head
        cur = dummy
        while cur.next is not None and cur.next.next is not None:
            start = cur.next
            end = cur.next.next
            cur.next = end
            start.next = end.next
            end.next = start
            cur = start
        return dummy.next

执行用时 : 44 ms
内存消耗 : 13.7 MB

参考

https://leetcode-cn.com/problems/swap-nodes-in-pairs/solution/hua-jie-suan-fa-24-liang-liang-jiao-huan-lian-biao/