Data Modelling & AI Data Structure & Algorithm

Insertion in Unrolled Linked List

21 June 2025

1

An unrolled linked list is a linked list of small arrays, all of the same size where each is so small that the insertion or deletion is fast and quick, but large enough to fill the cache line. An iterator pointing into the list consists of both a pointer to a node and an index into that node containing an array. It is also a data structure and is another variant of Linked List. It is related to B-Tree. It can store an array of elements at a node unlike a normal linked list which stores single element at a node. It is combination of arrays and linked list fusion-ed into one. It increases cache performance and decreases the memory overhead associated with storing reference for metadata. Other major advantages and disadvantages are already mentioned in the previous article.

Prerequisite : Introduction to Unrolled Linked List
Below is the insertion and display operation of Unrolled Linked List.

Input : 72 76 80 94 90 70
        capacity = 3
Output : Unrolled Linked List : 
72 76 
80 94 
90 70 

Explanation : The working is well shown in the
algorithm below. The nodes get broken at the 
mentioned capacity i.e., 3 here, when 3rd element 
is entered, the flow moves to another newly created 
node. Every node contains an array of size 
(int)[(capacity / 2) + 1]. Here it is 2. 


Input : 49 47 62 51 77 17 71 71 35 76 36 54
        capacity = 5
Output :
Unrolled Linked List : 
49 47 62 
51 77 17 
71 71 35 
76 36 54 

Explanation : The working is well shown in the
algorithm below. The nodes get broken at the
mentioned capacity i.e., 5 here, when 5th element
is entered, the flow moves to another newly 
created node. Every node contains an array of 
size (int)[(capacity / 2) + 1]. Here it is 3.

Algorithm :

Insert (ElementToBeInserted)
    if start_pos == NULL
        Insert the first element into the first node
        start_pos.numElement ++
        end_pos = start_pos
    If end_pos.numElements + 1 <  node_size
        end_pos.numElements.push(newElement)
        end_pos.numElements ++
    else
        create a new Node new_node
        move final half of end_pos.data into new_node.data
        new_node.data.push(newElement)
        end_pos.numElements = end_pos.data.size / 2 + 1
        end_pos.next = new_node
        end_pos = new_node

Implementation: Following is the Java implementation of the insertion and display operation. In the below code, the capacity is 5 and random numbers are input.

C++

// C++ program to show the insertion operation of Unrolled Linked List 
 
#include <iostream>
#include <cstdlib>
#include <ctime>
 
using namespace std;
 
// class for each node
class UnrollNode {
public:
    UnrollNode* next;
    int num_elements;
    int* array;
 
    // Constructor
    UnrollNode(int n)
    {
        next = nullptr;
        num_elements = 0;
        array = new int[n];
    }
};
 
// Operation of Unrolled Function
class UnrollLinkList {
 
private:
    UnrollNode* start_pos;
    UnrollNode* end_pos;
 
    int size_node;
    int nNode;
 
public:
    // Parameterized Constructor
    UnrollLinkList(int capacity)
    {
        start_pos = nullptr;
        end_pos = nullptr;
        nNode = 0;
        size_node = capacity + 1;
    }
 
    // Insertion operation
    void Insert(int num)
    {
        nNode++;
 
        // Check if the list starts from NULL
        if (start_pos == nullptr) {
            start_pos = new UnrollNode(size_node);
            start_pos->array[0] = num;
            start_pos->num_elements++;
            end_pos = start_pos;
            return;
        }
 
        // Attaching the elements into nodes
        if (end_pos->num_elements + 1 < size_node) {
            end_pos->array[end_pos->num_elements] = num;
            end_pos->num_elements++;
        }
 
        // Creation of new Node
        else {
            UnrollNode* node_pointer = new UnrollNode(size_node);
            int j = 0;
            for (int i = end_pos->num_elements / 2 + 1;
                 i < end_pos->num_elements; i++)
                node_pointer->array[j++] = end_pos->array[i];
 
            node_pointer->array[j++] = num;
            node_pointer->num_elements = j;
            end_pos->num_elements = end_pos->num_elements / 2 + 1;
            end_pos->next = node_pointer;
            end_pos = node_pointer;
        }
    }
 
    // Display the Linked List
    void display()
    {
        cout << "\nUnrolled Linked List = " << endl;
        UnrollNode* pointer = start_pos;
        while (pointer != nullptr) {
            for (int i = 0; i < pointer->num_elements; i++)
                cout << pointer->array[i] << " ";
            cout << endl;
            pointer = pointer->next;
        }
        cout << endl;
    }
};
 
// Main Class 
int main()
{
    srand(time(0));
 
    UnrollLinkList ull(5);
 
    // Perform Insertion Operation
    for (int i = 0; i < 12; i++) {
 
        // Generate random integers in range 0 to 99
        int rand_int1 = rand() % 100;
        cout << "Entered Element is " << rand_int1 << endl;
        ull.Insert(rand_int1);
        ull.display();
    }
    return 0;
}
 
// This code is contributed by Vikram_Shirsat

Python3

# Python program to show the insertion operation of Unrolled Linked List 
import random
 
# class for each node
class UnrollNode:
    def __init__(self, n):
        self.next = None
        self.num_elements = 0
        self.array = [0] * n
 
# Operation of Unrolled Function
class UnrollLinkList:
    def __init__(self, capacity):
        self.start_pos = None
        self.end_pos = None
        self.nNode = 0
        self.size_node = capacity + 1
 
    # Insertion operation
    def Insert(self, num):
        self.nNode += 1
         
        # Check if the list starts from NULL
        if self.start_pos is None:
            self.start_pos = UnrollNode(self.size_node)
            self.start_pos.array[0] = num
            self.start_pos.num_elements += 1
            self.end_pos = self.start_pos
            return
 
        # Attaching the elements into nodes
        if self.end_pos.num_elements + 1 < self.size_node:
            self.end_pos.array[self.end_pos.num_elements] = num
            self.end_pos.num_elements += 1
        # Creation of new Node
        else:
            node_pointer = UnrollNode(self.size_node)
            j = 0
            for i in range(self.end_pos.num_elements // 2 + 1, self.end_pos.num_elements):
                node_pointer.array[j] = self.end_pos.array[i]
                j += 1
            node_pointer.array[j] = num
            node_pointer.num_elements = j + 1
            self.end_pos.num_elements = self.end_pos.num_elements // 2 + 1
            self.end_pos.next = node_pointer
            self.end_pos = node_pointer
 
    # Display the Linked List
    def display(self):
        print("\nUnrolled Linked List = ")
        pointer = self.start_pos
        while pointer is not None:
            for i in range(pointer.num_elements):
                print(pointer.array[i], end=" ")
            print()
            pointer = pointer.next
        print()
 
# Main function
if __name__ == "__main__":
    ull = UnrollLinkList(5)
 
    # Perform Insertion Operation
    for i in range(12):
        # Generate random integers in range 0 to 99
        rand_int1 = random.randint(0, 99)
        print("Entered Element is ", rand_int1)
        ull.Insert(rand_int1)
        ull.display()
 
# This code is contributed by Vikram_Shirsat

C#

/* C# program to show the insertion operation
* of Unrolled Linked List */
using System;
 
// class for each node
public class UnrollNode {
    public UnrollNode next;
    public int num_elements;
    public int[] array;
 
    // Constructor
    public UnrollNode(int n)
    {
        next = null;
        num_elements = 0;
        array = new int[n];
    }
}
 
// Operation of Unrolled Function
public class UnrollLinkList {
 
    private UnrollNode start_pos;
    private UnrollNode end_pos;
 
    int size_node;
    int nNode;
 
    // Parameterized Constructor
    public UnrollLinkList(int capacity)
    {
        start_pos = null;
        end_pos = null;
        nNode = 0;
        size_node = capacity + 1;
    }
 
    // Insertion operation
    public void Insert(int num)
    {
        nNode++;
 
        // Check if the list starts from NULL
        if (start_pos == null) {
            start_pos = new UnrollNode(size_node);
            start_pos.array[0] = num;
            start_pos.num_elements++;
            end_pos = start_pos;
            return;
        }
 
        // Attaching the elements into nodes
        if (end_pos.num_elements + 1 < size_node) {
            end_pos.array[end_pos.num_elements] = num;
            end_pos.num_elements++;
        }
 
        // Creation of new Node
        else {
            UnrollNode node_pointer = new UnrollNode(size_node);
            int j = 0;
            for (int i = end_pos.num_elements / 2 + 1;
                 i < end_pos.num_elements; i++)
                node_pointer.array[j++] = end_pos.array[i];
 
            node_pointer.array[j++] = num;
            node_pointer.num_elements = j;
            end_pos.num_elements = end_pos.num_elements / 2 + 1;
            end_pos.next = node_pointer;
            end_pos = node_pointer;
        }
    }
 
    // Display the Linked List
    public void display()
    {
        Console.Write("\nUnrolled Linked List = ");
        Console.WriteLine();
        UnrollNode pointer = start_pos;
        while (pointer != null) {
            for (int i = 0; i < pointer.num_elements; i++)
                Console.Write(pointer.array[i] + " ");
            Console.WriteLine();
            pointer = pointer.next;
        }
        Console.WriteLine();
    }
}
 
/* Main Class */
public class UnrolledLinkedList_Check {
 
    // Driver code
    public static void Main(String[] args)
    {
        // create instance of Random class
        Random rand = new Random();
 
        UnrollLinkList ull = new UnrollLinkList(5);
 
        // Perform Insertion Operation
        for (int i = 0; i < 12; i++) {
 
            // Generate random integers in range 0 to 99
            int rand_int1 = rand.Next(100);
            Console.WriteLine("Entered Element is " + rand_int1);
            ull.Insert(rand_int1);
            ull.display();
        }
    }
}
 
// This code has been contributed by 29AjayKumar

Java

/* Java program to show the insertion operation
* of Unrolled Linked List */
import java.util.Scanner;
import java.util.Random;
 
// class for each node
class UnrollNode {
    UnrollNode next;
    int num_elements;
    int array[];
 
    // Constructor
    public UnrollNode(int n)
    {
        next = null;
        num_elements = 0;
        array = new int[n];
    }
}
 
// Operation of Unrolled Function
class UnrollLinkList {
 
    private UnrollNode start_pos;
    private UnrollNode end_pos;
 
    int size_node;
    int nNode;
 
    // Parameterized Constructor
    UnrollLinkList(int capacity)
    {
        start_pos = null;
        end_pos = null;
        nNode = 0;
        size_node = capacity + 1;
    }
 
    // Insertion operation
    void Insert(int num)
    {
        nNode++;
 
        // Check if the list starts from NULL
        if (start_pos == null) {
            start_pos = new UnrollNode(size_node);
            start_pos.array[0] = num;
            start_pos.num_elements++;
            end_pos = start_pos;
            return;
        }
 
        // Attaching the elements into nodes
        if (end_pos.num_elements + 1 < size_node) {
            end_pos.array[end_pos.num_elements] = num;
            end_pos.num_elements++;
        }
 
        // Creation of new Node
        else {
            UnrollNode node_pointer = new UnrollNode(size_node);
            int j = 0;
            for (int i = end_pos.num_elements / 2 + 1;
                 i < end_pos.num_elements; i++)
                node_pointer.array[j++] = end_pos.array[i];
 
            node_pointer.array[j++] = num;
            node_pointer.num_elements = j;
            end_pos.num_elements = end_pos.num_elements / 2 + 1;
            end_pos.next = node_pointer;
            end_pos = node_pointer;
        }
    }
 
    // Display the Linked List
    void display()
    {
        System.out.print("\nUnrolled Linked List = ");
        System.out.println();
        UnrollNode pointer = start_pos;
        while (pointer != null) {
            for (int i = 0; i < pointer.num_elements; i++)
                System.out.print(pointer.array[i] + " ");
            System.out.println();
            pointer = pointer.next;
        }
        System.out.println();
    }
}
 
/* Main Class */
class UnrolledLinkedList_Check {
 
    // Driver code
    public static void main(String args[])
    {
        Scanner sc = new Scanner(System.in);
 
        // create instance of Random class
        Random rand = new Random();
 
        UnrollLinkList ull = new UnrollLinkList(5);
 
        // Perform Insertion Operation
        for (int i = 0; i < 12; i++) {
 
            // Generate random integers in range 0 to 99
            int rand_int1 = rand.nextInt(100);
            System.out.println("Entered Element is " + rand_int1);
            ull.Insert(rand_int1);
            ull.display();
        }
    }
}

Javascript

<script>
/* Javascript program to show the insertion operation
* of Unrolled Linked List */
 
// class for each node
class UnrollNode 
{
    // Constructor
    constructor(n)
    {
        this.next = null;
        this.num_elements = 0;
        this.array = new Array(n);
        for(let i = 0; i < n; i++)
        {
            this.array[i] = 0;
        }
    }
}
 
// Operation of Unrolled Function
class UnrollLinkList
{
    // Parameterized Constructor
    constructor(capacity)
    {
        this.start_pos = null;
        this.end_pos = null;
        this.nNode = 0;
        this.size_node = capacity + 1;
         
    }
     
    // Insertion operation
    Insert(num)
    {
        this.nNode++;
   
        // Check if the list starts from NULL
        if (this.start_pos == null) {
            this.start_pos = new UnrollNode(this.size_node);
            this.start_pos.array[0] = num;
            this.start_pos.num_elements++;
            this.end_pos = this.start_pos;
            return;
        }
   
        // Attaching the elements into nodes
        if (this.end_pos.num_elements + 1 < this.size_node) {
            this.end_pos.array[this.end_pos.num_elements] = num;
            this.end_pos.num_elements++;
        }
   
        // Creation of new Node
        else {
            let node_pointer = new UnrollNode(this.size_node);
            let j = 0;
            for (let i = Math.floor(this.end_pos.num_elements / 2 )+ 1;
                 i < this.end_pos.num_elements; i++)
                node_pointer.array[j++] = this.end_pos.array[i];
   
            node_pointer.array[j++] = num;
            node_pointer.num_elements = j;
            this.end_pos.num_elements = Math.floor(this.end_pos.num_elements / 2) + 1;
            this.end_pos.next = node_pointer;
            this.end_pos = node_pointer;
        }
    }
     
    // Display the Linked List
    display()
    {
        document.write("<br>Unrolled Linked List = ");
        document.write("<br>");
        let pointer = this.start_pos;
        while (pointer != null) {
            for (let i = 0; i < pointer.num_elements; i++)
                document.write(pointer.array[i] + " ");
            document.write("<br>");
            pointer = pointer.next;
        }
        document.write("<br>");
    }
}
 
// Driver code
let ull = new UnrollLinkList(5);
 
 // Perform Insertion Operation
for (let i = 0; i < 12; i++)
{
 
    // Generate random integers in range 0 to 99
    let rand_int1 = Math.floor(Math.random()*(100));
    document.write("Entered Element is " + rand_int1+"<br>");
    ull.Insert(rand_int1);
    ull.display();
}
 
// This code is contributed by rag2127
</script>

Output

Entered Element is 67

Unrolled Linked List = 
67 

Entered Element is 69

Unrolled Linked List = 
67 69 

Entered Element is 50

Unrolled Linked List = 
67 69 50 

Entered Element is 60

Unrolled Linked List = 
67 69 50 60 

Entered Element is 18

Unrolled Linked List = 
67 69 50 60 18 

Entered Element is 15

Unrolled Linked List = 
67 69 50 
60 18 15 

Entered Element is 41

Unrolled Linked List = 
67 69 50 
60 18 15 41 

Entered Element is 79

Unrolled Linked List = 
67 69 50 
60 18 15 41 79 

Entered Element is 12

Unrolled Linked List = 
67 69 50 
60 18 15 
41 79 12 

Entered Element is 95

Unrolled Linked List = 
67 69 50 
60 18 15 
41 79 12 95 

Entered Element is 37

Unrolled Linked List = 
67 69 50 
60 18 15 
41 79 12 95 37 

Entered Element is 13

Unrolled Linked List = 
67 69 50 
60 18 15 
41 79 12 
95 37 13

Time complexity : O(n)
Also, few real-world applications :

It is used in B-Tree and T-Tree
Used in Hashed Array Tree
Used in Skip List
Used in CDR Coding

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Insertion in Unrolled Linked List

C++

Python3

C#

Java

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