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Reverse Nodes in k-Group

Explore how to reverse nodes in k-sized groups within a linked list by efficiently reordering nodes in-place. Understand constraints and methods that avoid extra memory usage, while preserving remaining nodes order and node values.

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Statement

The task is to reverse the nodes in groups of kk in a given linked list, where kk is a positive integer, and at most the length of the linked list. If any remaining nodes are not part of a group of kk, they should remain in their original order.

It is not allowed to change the values of the nodes in the linked list. Only the order of the nodes can be modified.

Note: Use only O(1)O(1) extra memory space.

Constraints:

Let n be the number of nodes in a linked list.

  • 1≤1 \leq k ≤\leq n ≤500\leq 500
  • 0≤0 \leq Node.value ≤1000\leq 1000

Examples

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Understand the problem

Let’s take a moment to make sure you’ve correctly understood the problem. The quiz below helps you check if you’re solving the correct problem:

Reverse Nodes in k-Group

1.

What is the output if the following head of the linked list and value of kk are given as input?

head → 8 → 0 → 6 → 1 → 0 → 7 → 8 → 7 → 5 → 3 → 5 → 2 → 4 → 9 → NULL

k = 3

A.

head → 1 → 0 → 7 → 8 → 0 → 6 → 3 → 5 → 2 → 8 → 7 → 5 → 4 → 9 → NULL

B.

head → 7 → 0 → 1 → 6 → 0 → 8 → 2 → 5 → 3 → 5 → 7 → 8 → 4 → 9 → NULL

C.

head → 6 → 0 → 8 → 7 → 0 → 1 → 5 → 7 → 8 → 2 → 5 → 3 → 4 → 9 → NULL

D.

head → 8 → 0 → 0 → 1 → 6 → 7 → 8 → 7 → 5 → 3 → 5 → 9 → 4 → 2 → NULL

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Figure it out!

We have a game for you to play. Rearrange the logical building blocks to develop a clearer understanding of how to solve this problem.

Sequence - Vertical
Drag and drop the cards to rearrange them in the correct sequence.
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Try it yourself

Implement your solution in the following coding playground.

Java
usercode > Solution.java
// Definition for a Linked List nod
// class ListNode {
//     int val;
//     ListNode next;
//     // Constructor
//     public ListNode(int val) {
//         this.val = val;
//         this.next = null;
//     }
// }
import java.util.*;
import ds_v1.LinkedList.ListNode;
public class Solution
{
    public static ListNode reverseKGroups(ListNode head, int k) {
        
        // Replace this placeholder return statement with your code
        return head;
    }
}
Reverse Nodes in k-Group