A linked list is a linear data structure that includes a series of connected nodes. Here, each node stores the data and the address of the next node. For example,
You have to start somewhere, so we give the address of the first node a special name called HEAD. Also, the last node in the linked list can be identified because its next portion points to NULL.
Linked lists can be of multiple types: singly, doubly, and circular linked list. In this article, we will focus on the singly linked list. To learn about other types, visit Types of Linked List.
Note: You might have played the game Treasure Hunt, where each clue includes the information about the next clue. That is how the linked list operates.
Representation of Linked List
Let's see how each node of the linked list is represented. Each node consists:
- A data item
- An address of another node
We wrap both the data item and the next node reference in a struct as:
struct node
{
int data;
struct node *next;
};
Understanding the structure of a linked list node is the key to having a grasp on it.
Each struct node has a data item and a pointer to another struct node. Let us create a simple Linked List with three items to understand how this works.
/* Initialize nodes */
struct node *head;
struct node *one = NULL;
struct node *two = NULL;
struct node *three = NULL;
/* Allocate memory */
one = malloc(sizeof(struct node));
two = malloc(sizeof(struct node));
three = malloc(sizeof(struct node));
/* Assign data values */
one->data = 1;
two->data = 2;
three->data=3;
/* Connect nodes */
one->next = two;
two->next = three;
three->next = NULL;
/* Save address of first node in head */
head = one;
If you didn't understand any of the lines above, all you need is a refresher on pointers and structs.
In just a few steps, we have created a simple linked list with three nodes.
The power of a linked list comes from the ability to break the chain and rejoin it. E.g. if you wanted to put an element 4 between 1 and 2, the steps would be:
- Create a new struct node and allocate memory to it.
- Add its data value as 4
- Point its next pointer to the struct node containing 2 as the data value
- Change the next pointer of "1" to the node we just created.
Doing something similar in an array would have required shifting the positions of all the subsequent elements.
In python and Java, the linked list can be implemented using classes as shown in the codes below.
Linked List Utility
Lists are one of the most popular and efficient data structures, with implementation in every programming language like C, C++, Python, Java, and C#.
Apart from that, linked lists are a great way to learn how pointers work. By practicing how to manipulate linked lists, you can prepare yourself to learn more advanced data structures like graphs and trees.
Linked List Implementations in Python, Java, C, and C++ Examples
# Linked list implementation in Python
class Node:
# Creating a node
def __init__(self, item):
self.item = item
self.next = None
class LinkedList:
def __init__(self):
self.head = None
if __name__ == '__main__':
linked_list = LinkedList()
# Assign item values
linked_list.head = Node(1)
second = Node(2)
third = Node(3)
# Connect nodes
linked_list.head.next = second
second.next = third
# Print the linked list item
while linked_list.head != None:
print(linked_list.head.item, end=" ")
linked_list.head = linked_list.head.next
// Linked list implementation in Java
class LinkedList {
// Creating a node
Node head;
static class Node {
int value;
Node next;
Node(int d) {
value = d;
next = null;
}
}
public static void main(String[] args) {
LinkedList linkedList = new LinkedList();
// Assign value values
linkedList.head = new Node(1);
Node second = new Node(2);
Node third = new Node(3);
// Connect nodess
linkedList.head.next = second;
second.next = third;
// printing node-value
while (linkedList.head != null) {
System.out.print(linkedList.head.value + " ");
linkedList.head = linkedList.head.next;
}
}
}
// Linked list implementation in C
#include <stdio.h>
#include <stdlib.h>
// Creating a node
struct node {
int value;
struct node *next;
};
// print the linked list value
void printLinkedlist(struct node *p) {
while (p != NULL) {
printf("%d ", p->value);
p = p->next;
}
}
int main() {
// Initialize nodes
struct node *head;
struct node *one = NULL;
struct node *two = NULL;
struct node *three = NULL;
// Allocate memory
one = malloc(sizeof(struct node));
two = malloc(sizeof(struct node));
three = malloc(sizeof(struct node));
// Assign value values
one->value = 1;
two->value = 2;
three->value = 3;
// Connect nodes
one->next = two;
two->next = three;
three->next = NULL;
// printing node-value
head = one;
printLinkedlist(head);
}
// Linked list implementation in C++
#include <bits/stdc++.h>
#include <iostream>
using namespace std;
// Creating a node
class Node {
public:
int value;
Node* next;
};
int main() {
Node* head;
Node* one = NULL;
Node* two = NULL;
Node* three = NULL;
// allocate 3 nodes in the heap
one = new Node();
two = new Node();
three = new Node();
// Assign value values
one->value = 1;
two->value = 2;
three->value = 3;
// Connect nodes
one->next = two;
two->next = three;
three->next = NULL;
// print the linked list value
head = one;
while (head != NULL) {
cout << head->value;
head = head->next;
}
}
Linked List Complexity
Time Complexity
| Worst case | Average Case | |
|---|---|---|
| Search | O(n) | O(n) |
| Insert | O(1) | O(1) |
| Deletion | O(1) | O(1) |
Space Complexity: O(n)
Linked List Applications
- Dynamic memory allocation
- Implemented in stack and queue
- In undo functionality of softwares
- Hash tables, Graphs