[LeetCode] Swapping Nodes in a Linked List

https://leetcode.com/problems/swapping-nodes-in-a-linked-list/

Swapping Nodes in a Linked List - LeetCode

문제 풀이 접근이 어려웠다.

왼쪽까지 움직이고 왼쪽부터 next가 null일 때까지 움직이면 right가 나오는 것을 캐치하면 풀 수 있는 문제

 

단순 val 바꿔주는 코드

class Solution:
    def swapNodes(self, head: Optional[ListNode], k: int) -> Optional[ListNode]:
        left = right = head
        for _ in range(k-1):
            left = left.next
            
        null_checker = left
        while null_checker.next:
            right = right.next
            null_checker = null_checker.next
            
        left.val, right.val = right.val, left.val
        return head

 

실제 노드 자체를 변경하는 코드

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:
    def swapNodes(self, head: Optional[ListNode], k: int) -> Optional[ListNode]:
        dummy = left_prev = right_prev = ListNode(next=head)
        left = right = head
        for _ in range(k-1):
            left_prev = left
            left = left.next
        
        null_checker = left
        while null_checker.next:
            null_checker = null_checker.next
            right_prev = right
            right = right.next
        if left == right:
            return head
        left_prev.next, right_prev.next = right, left
        left.next, right.next = right.next, left.next
        return dummy.next