LL: Reverse Between 해설

 

👩‍💻 문제

You are given a singly linked list and two integers start_index and end_index.

Your task is to write a method reverse_between within the LinkedList class that reverses the nodes of the linked list from start_index to  end_index (inclusive using 0-based indexing) in one pass and in-place.

Note: the Linked List does not have a tail which will make the implementation easier.

Assumption: You can assume that start_index and end_index are not out of bounds.

 

Input

• The method reverse_between takes two integer inputs start_index and end_index.
• The method will only be passed valid indexes (you do not need to test whether the indexes are out of bounds)

 

Output

• The method should modify the linked list in-place by reversing the nodes from start_index to  end_index.
• If the linked list is empty or has only one node, the method should return None.

 

💡 풀이

# WRITE REVERSE_BETWEEN METHOD HERE #
    def reverse_between(self, start_index, end_index):
        if self.length <= 1 :
            return self
        dummy = Node(0)
        dummy.next = self.head #cautious
        prev = dummy
        for _ in range(start_index):
            prev = prev.next
        current = prev.next
        for _ in range(end_index - start_index):
            after = current.next
            current.next = after.next
            after.next = prev.next
            prev.next = after
        self.head = dummy.next

 

 

✍️ 해설

 

 

🥳 배운점

 

역시 ... 손으로 그려가면서 풀어야 되는 거여써