연결 리스트¶

from typing import List 

class ListNode:
    def __init__(self, val=0, next=None):
        self.val = val
        self.next = next        

def printLinkedList(head: ListNode):
    while head:
        print(head.val)
        head = head.next

node_4 = ListNode(4)
node_3 = ListNode(3, node_4)
node_2 = ListNode(2, node_3)
node_1 = ListNode(1, node_2)

class Solution:
    def swapPairs(self, head: ListNode) -> ListNode:
        if head is None or head.next is None:
            return head
        cnt = 0
        cur = head
        nxt = head.next
        while nxt:
            if cnt == 0:
                cur.val, nxt.val = nxt.val, cur.val
                cnt += 1
            else:
                cnt = 0
            cur = nxt
            nxt = nxt.next
        
        return head

class Solution:
    def swapPairs(self, head: ListNode) -> ListNode:
        cur = head
        
        while cur and cur.next:
            cur.val, cur.next.val = cur.next.val, cur.val
            cur = cur.next.next
            
        return head

class Solution:
    def swapPairs(self, head: ListNode) -> ListNode:
        root = prev = ListNode(None)
        prev.next = head
        
        while head and head.next:
            b = head.next
            head.next = b.next
            b.next = head
            
            prev.next = b
            
            head = head.next
            prev = prev.next.next
            
        return root.next

class Solution:
    def swapPairs(self, head: ListNode) -> ListNode:
        if head and head.next:
            p = head.next
            
            head.next = self.swapPairs(p.next)
            p.next = head
            return p
        return head