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

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

## 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(); } } }

**Output:**

Entered Element is 90 Unrolled Linked List = 90 Entered Element is 3 Unrolled Linked List = 90 3 Entered Element is 12 Unrolled Linked List = 90 3 12 Entered Element is 43 Unrolled Linked List = 90 3 12 43 Entered Element is 88 Unrolled Linked List = 90 3 12 43 88 Entered Element is 94 Unrolled Linked List = 90 3 12 43 88 94 Entered Element is 15 Unrolled Linked List = 90 3 12 43 88 94 15 Entered Element is 7 Unrolled Linked List = 90 3 12 43 88 94 15 7 Entered Element is 67 Unrolled Linked List = 90 3 12 43 88 94 15 7 67 Entered Element is 74 Unrolled Linked List = 90 3 12 43 88 94 15 7 67 74 Entered Element is 85 Unrolled Linked List = 90 3 12 43 88 94 15 7 67 74 85 Entered Element is 48 Unrolled Linked List = 90 3 12 43 88 94 15 7 67 74 85 48

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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