Unrolled Linked List | Set 1 (Introduction)

Like array and linked list, unrolled Linked List is also a linear data structure and is a variant of linked list. Unlike simple linked list, it stores multiple elements at each node. That is, instead of storing single element at a node, unrolled linked lists store an array of elements at a node. Unrolled linked list covers advantages of both array and linked list as it reduces the memory overhead in comparison to simple linked lists by storing multiple elements at each node and it also has the advantage of fast insertion and deletion as that of a linked list.

unrolledlinkedlist

Advantages:

  • Because of the Cache behavior, linear search is much faster in unrolled linked lists.
  • In comparison to ordinary linked list, it requires less storage space for pointers/references.
  • It performs operations like insertion, deletion and traversal more quickly than ordinary linked lists (because search is faster).

Disadvantages:

  • The overhead per node is comparatively high than singly linked lists. Refer an example node in below code.

Simple Implementation in C
The below program creates a simple unrolled linked list with 3 nodes containing variable number of elements in each. It also traverses the created list.

// C program to implement unrolled linked list
// and traversing it.
#include<stdio.h>
#include<stdlib.h>
#define maxElements 4

// Unrolled Linked List Node
struct Node
{
    int numElements;
    int array[maxElements];
    struct Node *next;
};

/* Function to traverse am unrolled linked list
   and print all the elements*/
void printUnrolledList(struct Node *n)
{
    while (n != NULL)
    {
        // Print elements in current node
        for (int i=0; i<n->numElements; i++)
            printf("%d ", n->array[i]);

        // Move to next node 
        n = n->next;
    }
}

// Program to create an unrolled linked list
// with 3 Nodes
int main()
{
    struct Node* head = NULL;
    struct Node* second = NULL;
    struct Node* third = NULL;

    // allocate 3 Nodes
    head = (struct Node*)malloc(sizeof(struct Node));
    second = (struct Node*)malloc(sizeof(struct Node));
    third = (struct Node*)malloc(sizeof(struct Node));

    // Let us put some values in second node (Number
    // of values must be less than or equal to
    // maxElement)
    head->numElements = 3;
    head->array[0] = 1;
    head->array[1] = 2;
    head->array[2] = 3;

    // Link first Node with the second Node
    head->next = second;

    // Let us put some values in second node (Number
    // of values must be less than or equal to
    // maxElement)
    second->numElements = 3;
    second->array[0] = 4;
    second->array[1] = 5;
    second->array[2] = 6;

    // Link second Node with the third Node
    second->next = third;

    // Let us put some values in third node (Number
    // of values must be less than or equal to
    // maxElement)
    third->numElements = 3;
    third->array[0] = 7;
    third->array[1] = 8;
    third->array[2] = 9;
    third->next = NULL;

    printUnrolledList(head);

    return 0;
}

Output:

1 2 3 4 5 6 7 8 9

In this article, we have introduced unrolled list and advantages of it. We have also shown how to traverse the list. In the next article, we will be discussing insertion, deletion and values of maxElements/numElements in detail.

This article is contributed by Harsh Agarwal. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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