24. 两两交换链表中的节点 (Python 实现)

x33g5p2x  于2022-07-06 转载在 Python  
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题目:
给你一个链表,两两交换其中相邻的节点,并返回交换后链表的头节点。你必须在不修改节点内部的值的情况下完成本题(即,只能进行节点交换)。

示例 1:

输入:head = [1,2,3,4]
输出:[2,1,4,3]

示例 2:

输入:head = []
输出:[]

示例 3:

输入:head = [1]
输出:[1]

代码:

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:
    def swapPairs(self, head: ListNode) -> ListNode:
        if head == None or head.next == None:
            return head
        res = ListNode()
        res.next = head
        temp = res
        while temp.next and temp.next.next:
            a, b = temp.next, temp.next.next
            temp.next = b
            a.next = b.next
            b.next = a
            temp = a
        return res.next

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