[리트코드 leetcode] 24. Swap Nodes in Pairs

leetcode.com/problems/swap-nodes-in-pairs/

Swap Nodes in Pairs - LeetCode

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leetcode.com

# 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 and head.next :
            next = ListNode(head.val, head.next.next)
            node = ListNode(head.next.val,next)
            node.next.next = self.swapPairs(head.next.next)
            return node
        
        return head

# 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 not head or not head.next:
            return head
        
        if head and head.next.next:
            head.next.next = self.swapPairs(head.next.next)    
        
        prev = head.next
        head.next = head.next.next
        prev.next = head
        return prev