24. Swap Nodes in Pairs - python

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

Swap Nodes in Pairs - LeetCode

 

 

노드를 순회 하면서 2개씩 리스트에 넣고 2개가 채워지면 다시 리스트에 넣어 이중 리스트를 만든다 
2개씩 들어있는 리스트의 순서를 바꿔야하니까 
넣은 순서대로 꺼내준다 

 

# 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: Optional[ListNode]) -> Optional[ListNode]:
        p=[]
        i=0
        t=[]
        while True:
            
            if i%2==0:
                if t:
                    p.append(t)
                t=[] 
            if not head:
                break
            t.append(head.val)
            #p.append(head.val)
            head=head.next
            i+=1
        if t:
            p.append(t)
        h=None
        print(p)
        while p:
            for i in p.pop():
                if not h:
                    h=ListNode(i)
                else:
                    h=ListNode(i,h)
        return h