Partition a Linked List into K continuous groups with difference in their sizes at most 1

Given a linked list consisting of N nodes and an integer K, the task is to split the given Linked List into K continuous groups such that the difference between the size of the adjacent groups after splitting is at most 1 and the groups are sorted in descending order of their lengths. 

Note: A group with 0 elements can also be formed.

Examples:

Input: 1 → 2 → 3 → 4, K = 5
Output: {{1}, {2}, {3}, {4}, {}}
Explanation: Required splits are {{1 -> NULL}, {2 -> NULL}, {3 -> NULL}, {4 -> NULL}, {NULL}}.

Input: LL: 1 → 2 → 3 → 4 → 5 → 6 → 7 → 8, K = 3
Output: {{1, 2, 3}, {4, 5, 6}, {7, 8}}

Approach: The given problem can be solved based on the observation that forming first N % K groups of size (N / K + 1) and the remaining K – (N % K) groups of size N / K satisfies the conditions. Follow the steps below to solve the problem:

• Initialize a vector of the linked list, says ans, that stores the K groups.
• Store the value of N / K and N % K in the variables, say L and R.
• Traverse the given linked list and perform the following steps:
  • Store the value of L in a variable say X and the value of head in the variable say currHead and last.
  • If the value of R is positive, then update the value of head to head->next.
  • Iterate a loop until X is non-zero and perform the following steps:
    • If the last node is the same as the head node then move the head node to the next node.
    • Otherwise, join the links between the last node and the head node and update the last to head, and move the head node to the next node.
    • Push the current Linked List as the currentHead in the vector ans[].
• If the value of K is greater than 0, then push the NULL Linked List in ans and decrement K by 1.
• After completing the above steps, print the elements of all the Linked List stored in the vector ans[].

Below is the implementation of the above approach:

C++

// C++ program for the above approach

#include <bits/stdc++.h>
using namespace std;

// Link List Node
struct ListNode {
    int val;
    struct ListNode* next;
};

// Function to insert a node
// into the Linked List
void push(ListNode** head_ref,
          int node_val)
{
    // Allocate a new dynamic node
    ListNode* new_node = new ListNode();

    // Update new_node->val
    new_node->val = node_val;

    // Stores the head_ref
    new_node->next = (*head_ref);

    // Update (*head_ref)
    (*head_ref) = new_node;
}

// Function to split the linked list
// in K groups
void splitListInParts(ListNode* head,
                      int K)
{
    // Stores the K groups
    vector<ListNode*> ans;

    // If head is NULL
    if (!head) {

        // Iterate until K is non-zero
        while (K--)
            ans.push_back(NULL);
    }

    // Stores the length of the
    // linked list
    int N = 0;

    // Stores the head node of the
    // linked list
    ListNode* p = head;

    // Iterate over the linked list
    while (p) {

        // Update p
        p = p->next;

        // Update N
        N++;
    }

    int len = N / K;
    int rem = N % K;

    p = head;

    // Iterate over the linked list
    while (K > 0 && p) {

        // Stores the length
        // of the current group
        int x = len;

        // Stores the current node
        ListNode* curr_head = p;

        // Stores the previous node
        ListNode* last = p;

        // If rem is greater than 0
        if (rem > 0) {

            // Update p
            p = p->next;

            // Decrement rem by 1
            rem--;
        }

        // Iterate until x is non-zero
        while (x--) {

            // If the last is equal to p
            if (last == p)
                p = p->next;

            // Otherwise
            else {

                // Join the link between
                // last and the current
                // element
                last->next = p;

                // Update the last node
                last = p;

                // Update p node
                p = p->next;
            }
        }

        // Assign NULL to last->next
        last->next = NULL;

        // Push the current linked
        // list in ans
        ans.push_back(curr_head);

        // Decrement K
        K--;
    }

    // While K greater than 0
    while (K > 0) {

        // Update the value of ans
        ans.push_back(NULL);

        // Increment K
        K--;
    }

    // Print the result
    cout << "{";
    for (int i = 0; i < ans.size(); i++) {
        cout << "{";

        while (ans[i]) {

            // Print the value
            cout << ans[i]->val << "  ";

            // Update ans[i]
            ans[i] = ans[i]->next;
        }
        cout << "}";
        if (i != ans.size() - 1)
            cout << ", ";
    }
    cout << "}";
}

// Driver Code
int main()
{
    ListNode* root = NULL;
    push(&root, 8);
    push(&root, 7);
    push(&root, 6);
    push(&root, 5);
    push(&root, 4);
    push(&root, 3);
    push(&root, 2);
    push(&root, 1);
    int K = 3;

    splitListInParts(root, K);

    return 0;
}

Java

// Java program for the above approach
import java.util.*;

class GFG{

// Link List Node
static class ListNode
{
    int val;
    ListNode next;
};

// Function to insert a node
// into the Linked List
static ListNode push(ListNode head_ref,
                     int node_val)
{

    // Allocate a new dynamic node
    ListNode new_node = new ListNode();

    // Update new_node.val
    new_node.val = node_val;

    // Stores the head_ref
    new_node.next = head_ref;

    // Update head_ref
    head_ref = new_node;
    return head_ref;
}

// Function to split the linked list
// in K groups
static void splitListInParts(ListNode head,
                             int K)
{

    // Stores the K groups
    Vector<ListNode> ans = new Vector<ListNode>();

    // If head is null
    if (head == null)
    {

        // Iterate until K is non-zero
        while (K-- > 0)
            ans.add(null);
    }

    // Stores the length of the
    // linked list
    int N = 0;

    // Stores the head node of the
    // linked list
    ListNode p = head;

    // Iterate over the linked list
    while (p.next != null)
    {

        // Update p
        p = p.next;

        // Update N
        N++;
    }

    int len = N / K;
    int rem = N % K;

    p = head;

    // Iterate over the linked list
    while (K > 0 && p.next != null)
    {

        // Stores the length
        // of the current group
        int x = len;

        // Stores the current node
        ListNode curr_head = p;

        // Stores the previous node
        ListNode last = p;

        // If rem is greater than 0
        if (rem > 0)
        {

            // Update p
            p = p.next;

            // Decrement rem by 1
            rem--;
        }

        // Iterate until x is non-zero
        while (x-- > 0)
        {

            // If the last is equal to p
            if (last == p)
                p = p.next;

            // Otherwise
            else
            {

                // Join the link between
                // last and the current
                // element
                last.next = p;

                // Update the last node
                last = p;

                // Update p node
                p = p.next;
            }
        }

        // Assign null to last.next
        last.next = null;

        // Push the current linked
        // list in ans
        ans.add(curr_head);

        // Decrement K
        K--;
    }

    // While K greater than 0
    while (K > 0)
    {

        // Update the value of ans
        ans.add(null);

        // Increment K
        K--;
    }

    // Print the result
    System.out.print("{");
    for(int i = 0; i < ans.size(); i++)
    {
        System.out.print("{");

        while (ans.get(i) != null)
        {

            // Print the value
            System.out.print(ans.get(i).val + "  ");

            // Update ans[i]
            ans.set(i, ans.get(i).next);

        }
        System.out.print("}");
        if (i != ans.size() - 1)
            System.out.print(", ");
    }
    System.out.print("}");
}

// Driver Code
public static void main(String[] args)
{
    ListNode root = new ListNode();
    root = push(root, 8);
    root = push(root, 7);
    root = push(root, 6);
    root = push(root, 5);
    root = push(root, 4);
    root = push(root, 3);
    root = push(root, 2);
    root = push(root, 1);
    int K = 3;

    splitListInParts(root, K);
}
}

// This code is contributed by shikhasingrajput

C#

// C# program for the above approach
using System;
using System.Collections.Generic;

public class GFG{

// Link List Node
class ListNode
{
    public int val;
    public ListNode next;
};

// Function to insert a node
// into the Linked List
static ListNode push(ListNode head_ref,
                     int node_val)
{

    // Allocate a new dynamic node
    ListNode new_node = new ListNode();

    // Update new_node.val
    new_node.val = node_val;

    // Stores the head_ref
    new_node.next = head_ref;

    // Update head_ref
    head_ref = new_node;
    return head_ref;
}

// Function to split the linked list
// in K groups
static void splitListInParts(ListNode head,
                             int K)
{

    // Stores the K groups
    List<ListNode> ans = new List<ListNode>();

    // If head is null
    if (head == null)
    {

        // Iterate until K is non-zero
        while (K-- > 0)
            ans.Add(null);
    }

    // Stores the length of the
    // linked list
    int N = 0;

    // Stores the head node of the
    // linked list
    ListNode p = head;

    // Iterate over the linked list
    while (p.next != null)
    {

        // Update p
        p = p.next;

        // Update N
        N++;
    }

    int len = N / K;
    int rem = N % K;

    p = head;

    // Iterate over the linked list
    while (K > 0 && p.next != null)
    {

        // Stores the length
        // of the current group
        int x = len;

        // Stores the current node
        ListNode curr_head = p;

        // Stores the previous node
        ListNode last = p;

        // If rem is greater than 0
        if (rem > 0)
        {

            // Update p
            p = p.next;

            // Decrement rem by 1
            rem--;
        }

        // Iterate until x is non-zero
        while (x-- > 0)
        {

            // If the last is equal to p
            if (last == p)
                p = p.next;

            // Otherwise
            else
            {

                // Join the link between
                // last and the current
                // element
                last.next = p;

                // Update the last node
                last = p;

                // Update p node
                p = p.next;
            }
        }

        // Assign null to last.next
        last.next = null;

        // Push the current linked
        // list in ans
        ans.Add(curr_head);

        // Decrement K
        K--;
    }

    // While K greater than 0
    while (K > 0)
    {

        // Update the value of ans
        ans.Add(null);

        // Increment K
        K--;
    }

    // Print the result
    Console.Write("{");
    for(int i = 0; i < ans.Count; i++)
    {
        Console.Write("{");

        while (ans[i] != null)
        {

            // Print the value
            Console.Write(ans[i].val + "  ");

            // Update ans[i]
            ans[i] = ans[i].next;

        }
        Console.Write("}");
        if (i != ans.Count - 1)
            Console.Write(", ");
    }
    Console.Write("}");
}

// Driver Code
public static void Main(String[] args)
{
    ListNode root = new ListNode();
    root = push(root, 8);
    root = push(root, 7);
    root = push(root, 6);
    root = push(root, 5);
    root = push(root, 4);
    root = push(root, 3);
    root = push(root, 2);
    root = push(root, 1);
    int K = 3;

    splitListInParts(root, K);
}
}



// This code contributed by shikhasingrajput

Javascript

<script>


// javascript program for the above approach

// Link List Node
class ListNode {

    constructor()
    {
        this.val = 0;
        this.next = null;
    }
};

// Function to insert a node
// into the Linked List
function pushIn(head_ref, node_val)
{
    // Allocate a new dynamic node
    var new_node = new ListNode();

    // Update new_node.val
    new_node.val = node_val;

    // Stores the head_ref
    new_node.next = (head_ref);

    // Update (*head_ref)
    head_ref = new_node;

    return head_ref;
}

// Function to split the linked list
// in K groups
function splitListInParts(head, K)
{
    // Stores the K groups
    var ans = [];

    // If head is null
    if (!head) {

        // Iterate until K is non-zero
        while (K--)
            ans.push(null);
    }

    // Stores the length of the
    // linked list
    var N = 0;

    // Stores the head node of the
    // linked list
    var p = head;

    // Iterate over the linked list
    while (p) {

        // Update p
        p = p.next;

        // Update N
        N++;
    }

    var len = parseInt(N / K);
    var rem = N % K;

    p = head;

    // Iterate over the linked list
    while (K > 0 && p) {

        // Stores the length
        // of the current group
        var x = len;

        // Stores the current node
        var curr_head = p;

        // Stores the previous node
        var last = p;

        // If rem is greater than 0
        if (rem > 0) {

            // Update p
            p = p.next;

            // Decrement rem by 1
            rem--;
        }

        // Iterate until x is non-zero
        while (x--) {

            // If the last is equal to p
            if (last == p)
                p = p.next;

            // Otherwise
            else {

                // Join the link between
                // last and the current
                // element
                last.next = p;

                // Update the last node
                last = p;

                // Update p node
                p = p.next;
            }
        }

        // Assign null to last.next
        last.next = null;

        // Push the current linked
        // list in ans
        ans.push(curr_head);

        // Decrement K
        K--;
    }

    // While K greater than 0
    while (K > 0) {

        // Update the value of ans
        ans.push(null);

        // Increment K
        K--;
    }

    // Print the result
    document.write( "{");
    for (var i = 0; i < ans.length; i++) {
        document.write( "{");

        while (ans[i]) {

            // Print the value
            document.write( ans[i].val + "  ");

            // Update ans[i]
            ans[i] = ans[i].next;
        }
        document.write( "}");
        if (i != ans.length - 1)
            document.write( ", ");
    }
    document.write( "}");
}

// Driver Code
var root = null;
root = pushIn(root, 8);
root = pushIn(root, 7);
root = pushIn(root, 6);
root = pushIn(root, 5);
root = pushIn(root, 4);
root = pushIn(root, 3);
root = pushIn(root, 2);
root = pushIn(root, 1);
var K = 3;
splitListInParts(root, K);

// This code is contributed by rrrtnx.
</script>

Output:

{{1  2  3  }, {4  5  6  }, {7  8  }}

Time Complexity: O(N)
Auxiliary Space: O(N)