In this article we discusses about Singly Link List Data Structure. If arrays adjust similar types of data types, linked lists consist of elements with different data types that are also arranged sequentially.
But how are these linked lists created?
A linked list is a collection of “nodes” connected together via links. These nodes consist of the data to be stored and a pointer to the address of the next node within the linked list. In the case of arrays, the size is limited to the definition, but in linked lists, there is no defined size. Any amount of data can be stored in it and can be deleted from it.
Singly Link List
Singly linked lists contain two “buckets” in one node; one bucket holds the data and the other bucket holds the address of the next node of the list. Traversals can be done in one direction only as there is only a single link between two nodes of the same list.
Basic Operations of Singly Link List
The basic operations in the linked lists are insertion, deletion, searching, display, and deleting an element at a given key. These operations are performed on Singly Link List as given below −
- Insertion − Adds an element at the beginning of the list.
- Deletion − Deletes an element at the beginning of the list.
- Display − Displays the complete list.
- Search − Searches an element using the given key.
- Delete − Deletes an element using the given key.
Insertion Operation
Adding a new node in link list is a more than one step activity. We shall learn this with diagrams here. First, create a node using the same structure and find the location where it has to be inserted.
Imagine that we are inserting a node B (NewNode), between A (LeftNode) and C (RightNode). Then point B.next to C −
NewNode.next −> RightNode;It should look like this −
Now, the next node at the left should point to the new node.LeftNode.next −> NewNode;
This will put the new node in the middle of the two. The new list should look like this −
Insertion in link list can be done in three different ways.
Insertion at Beginning
In this operation, we are adding an element at the beginning of the list.
Algorithm
- START
- Create a node to store the data.
- Check if the list is empty.
- If the list is empty, add the data to the node and assign the head pointer to it.
- If the list is not empty, add the data to a node and link to the current head.
- Assign the head to the newly added node.
- END
Example
#include <iostream>
using namespace std;
struct node {
int data;
struct node *next;
};
struct node *head = NULL;
struct node *current = NULL;
// display the list
void printList(){
struct node *p = head;
cout << "\n[";
//start from the beginning
while(p != NULL) {
cout << " " << p->data << " ";
p = p->next;
}
cout << "]";
}
//insertion at the beginning
void insertatbegin(int data){
//create a link
struct node *lk = (struct node*) malloc(sizeof(struct node));
lk->data = data;
// point it to old first node
lk->next = head;
//point first to new first node
head = lk;
}
int main(){
insertatbegin(12);
insertatbegin(22);
insertatbegin(30);
insertatbegin(44);
cout << "Linked List: ";
// print list
printList();
}Insertion at Ending
In this operation, we are adding an element at the ending of the list.
Algorithm
- START.
- Create a new node and assign the data.
- Find the last node.
- Point the last node to new node.
- END
Example
#include <iostream>
using namespace std;
struct node {
int data;
struct node *next;
};
struct node *head = NULL;
struct node *current = NULL;
// display the list
void printList(){
struct node *p = head;
cout << "\n[";
//start from the beginning
while(p != NULL) {
cout << " " << p->data << " ";
p = p->next;
}
cout << "]";
}
//insertion at the beginning
void insertatbegin(int data){
//create a link
struct node *lk = (struct node*) malloc(sizeof(struct node));
lk->data = data;
// point it to old first node
lk->next = head;
//point first to new first node
head = lk;
}
void insertatend(int data){
//create a link
struct node *lk = (struct node*) malloc(sizeof(struct node));
lk->data = data;
struct node *linkedlist = head;
// point it to old first node
while(linkedlist->next != NULL)
linkedlist = linkedlist->next;
//point first to new first node
linkedlist->next = lk;
}
int main(){
insertatbegin(12);
insertatend(22);
insertatbegin(30);
insertatend(44);
insertatbegin(50);
cout << "Linked List: ";
// print list
printList();
}Insertion at a Given Position
In this operation, we are adding an element at any position within the list.
Algorithm
- START.
- Create a new node and assign data to it.
- Iterate until the node at position is found.
- Point first to new first node.
- END
Example
#include <iostream>
using namespace std;
struct node {
int data;
struct node *next;
};
struct node *head = NULL;
struct node *current = NULL;
// display the list
void printList(){
struct node *p = head;
cout << "\n[";
//start from the beginning
while(p != NULL) {
cout << " " << p->data << " ";
p = p->next;
}
cout << "]";
}
//insertion at the beginning
void insertatbegin(int data){
//create a link
struct node *lk = (struct node*) malloc(sizeof(struct node));
lk->data = data;
// point it to old first node
lk->next = head;
//point first to new first node
head = lk;
}
void insertafternode(struct node *list, int data){
struct node *lk = (struct node*) malloc(sizeof(struct node));
lk->data = data;
lk->next = list->next;
list->next = lk;
}
int main(){
insertatbegin(12);
insertatbegin(22);
insertatbegin(30);
insertafternode(head->next,44);
insertafternode(head->next->next, 50);
cout << "Linked List: ";
// print list
printList();
}Deletion Operation
Deletion is also a more than one step process. We shall learn with pictorial representation. First, locate the target node to be removed, by using searching algorithms.
The left (previous) node of the target node now should point to the next node of the target node −LeftNode.next −> TargetNode.next;
This will remove the link that was pointing to the target node. Now, using the following code, we will remove what the target node is pointing at.TargetNode.next −> NULL;
We need to use the deleted node. We can keep that in memory otherwise we can simply deallocate memory and wipe off the target node completely.
Similar steps should be taken if the node is being inserted at the beginning of the list. While inserting it at the end, the second last node of the list should point to the new node and the new node will point to NULL.
Deletion in linked lists is also performed in three different ways.
Deletion at Beginning
In this deletion operation of the linked, we are deleting an element from the beginning of the list. For this, we point the head to the second node.
Algorithm
- START.
- Assign the head pointer to the next node in the list.
- END
Example
#include <iostream>
using namespace std;
struct node {
int data;
struct node *next;
};
struct node *head = NULL;
struct node *current = NULL;
// display the list
void printList(){
struct node *p = head;
cout << "\n[";
//start from the beginning
while(p != NULL) {
cout << " " << p->data << " ";
p = p->next;
}
cout << "]";
}
//insertion at the beginning
void insertatbegin(int data){
//create a link
struct node *lk = (struct node*) malloc(sizeof(struct node));
lk->data = data;
// point it to old first node
lk->next = head;
//point first to new first node
head = lk;
}
void deleteatbegin(){
head = head->next;
}
int main(){
insertatbegin(12);
insertatbegin(22);
insertatbegin(30);
insertatbegin(44);
insertatbegin(50);
cout << "Linked List: ";
// print list
printList();
deleteatbegin();
cout << "Linked List after deletion: ";
printList();
} Deletion at Ending
In this deletion operation of the linked, we are deleting an element from the ending of the list.
Algorithm
- START
- Iterate until you find the second last element in the list.
- Assign NULL to the second last element in the list.
- END
Example
#include <iostream>
using namespace std;
struct node {
int data;
struct node *next;
};
struct node *head = NULL;
struct node *current = NULL;
// Displaying the list
void printList(){
struct node *p = head;
while(p != NULL) {
cout << " " << p->data << " ";
p = p->next;
}
}
// Insertion at the beginning
void insertatbegin(int data){
//create a link
struct node *lk = (struct node*) malloc(sizeof(struct node));
lk->data = data;
// point it to old first node
lk->next = head;
//point first to new first node
head = lk;
}
void deleteatend(){
struct node *linkedlist = head;
while (linkedlist->next->next != NULL)
linkedlist = linkedlist->next;
linkedlist->next = NULL;
}
int main(){
insertatbegin(12);
insertatbegin(22);
insertatbegin(30);
insertatbegin(44);
insertatbegin(50);
cout << "Linked List: ";
// print list
printList();
deleteatend();
cout << "\nLinked List after deletion: ";
printList();
}Deletion at a Given Position
In this deletion operation of the linked, we are deleting an element at any position of the list.
Algorithm
- START
- Iterate until find the current node at position in the list
- Assign the adjacent node of current node in the list to its previous node.
- END
Example
#include <iostream>
using namespace std;
struct node {
int data;
struct node *next;
};
struct node *head = NULL;
struct node *current = NULL;
// display the list
void printList(){
struct node *p = head;
cout << "\n[";
//start from the beginning
while(p != NULL) {
cout << " " << p->data << " ";
p = p->next;
}
cout << "]";
}
//insertion at the beginning
void insertatbegin(int data){
//create a link
struct node *lk = (struct node*) malloc(sizeof(struct node));
lk->data = data;
// point it to old first node
lk->next = head;
//point first to new first node
head = lk;
}
void deletenode(int key){
struct node *temp = head, *prev;
if (temp != NULL && temp->data == key) {
head = temp->next;
return;
}
// Find the key to be deleted
while (temp != NULL && temp->data != key) {
prev = temp;
temp = temp->next;
}
// If the key is not present
if (temp == NULL) return;
// Remove the node
prev->next = temp->next;
}
int main(){
insertatbegin(12);
insertatbegin(22);
insertatbegin(30);
insertatbegin(44);
insertatbegin(50);
cout << "Linked List: ";
// print list
printList();
deletenode(30);
cout << "Linked List after deletion: ";
printList();
} Reverse Operation
This operation is a thorough one. We need to make the last node to be pointed by the head node and reverse the whole linked list.
First, we traverse to the end of the list. It should be pointing to NULL. Now, we shall make it point to its previous node −
We have to make sure that the last node is not the last node. So we’ll have some temp node, which looks like the head node pointing to the last node. Now, we shall make all left side nodes point to their previous nodes one by one.
Except the node (first node) pointed by the head node, all nodes should point to their predecessor, making them their new successor. The first node will point to NULL.
We’ll make the head node point to the new first node by using the temp node.
Algorithm
Step by step process to reverse a linked list is as follow
- START
- We use three pointers to perform the reversing: prev, next, head.
- Point the current node to head and assign its next value to the prev node.
- Iteratively repeat the step 3 for all the nodes in the list.
- Assign head to the prev node.
Example
#include <iostream>
struct node {
int data;
struct node *next;
};
struct node *head = NULL;
struct node *current = NULL;
// display the list
void printList(){
struct node *p = head;
printf("\n[");
//start from the beginning
while(p != NULL) {
printf(" %d ",p->data);
p = p->next;
}
printf("]");
}
//insertion at the beginning
void insertatbegin(int data){
//create a link
struct node *lk = (struct node*) malloc(sizeof(struct node));
lk->data = data;
// point it to old first node
lk->next = head;
//point first to new first node
head = lk;
}
void reverseList(struct node** head){
struct node *prev = NULL, *cur=*head, *tmp;
while(cur!= NULL) {
tmp = cur->next;
cur->next = prev;
prev = cur;
cur = tmp;
}
*head = prev;
}
int main(){
int k=0;
insertatbegin(12);
insertatbegin(22);
insertatbegin(30);
insertatbegin(40);
insertatbegin(55);
printf("Linked List: ");
// print list
printList();
reverseList(&head);
printf("\nReversed Linked List: ");
printList();
return 0;
}Search Operation
Searching for an element in the list using a key element. This operation is done in the same way as array search; comparing every element in the list with the key element given.
Algorithm
- START
- If the list is not empty, iteratively check if the list contains the key
- If the key element is not present in the list, unsuccessful search
- END
Example
#include <iostream>
using namespace std;
struct node {
int data;
struct node *next;
};
struct node *head = NULL;
struct node *current = NULL;
// display the list
void printList(){
struct node *p = head;
cout << "\n[";
//start from the beginning
while(p != NULL) {
cout << " " << p->data << " ";
p = p->next;
}
cout << "]";
}
//insertion at the beginning
void insertatbegin(int data){
//create a link
struct node *lk = (struct node*) malloc(sizeof(struct node));
lk->data = data;
// point it to old first node
lk->next = head;
//point first to new first node
head = lk;
}
int searchlist(int key){
struct node *temp = head;
while(temp != NULL) {
if (temp->data == key) {
return 1;
}
temp=temp->next;
}
return 0;
}
int main(){
int k = 0;
insertatbegin(12);
insertatbegin(22);
insertatbegin(30);
insertatbegin(44);
insertatbegin(50);
cout << "Linked List: ";
// print list
printList();
k = searchlist(16);
if (k == 1)
cout << "\nElement is found";
else
cout << "\nElement is not present in the list";
}Traversal Operation
The traversal operation walks through all the elements of the list in an order and displays the elements in that order.
Algorithm
- START
- While the list is not empty and did not reach the end of the list, print the data in each node
- END
Example
#include <iostream>
using namespace std;
struct node {
int data;
struct node *next;
};
struct node *head = NULL;
struct node *current = NULL;
// Displaying the list
void printList(){
struct node *p = head;
while(p != NULL) {
cout << " " << p->data << " ";
p = p->next;
}
}
// Insertion at the beginning
void insertatbegin(int data){
//create a link
struct node *lk = (struct node*) malloc(sizeof(struct node));
lk->data = data;
// point it to old first node
lk->next = head;
//point first to new first node
head = lk;
}
int main(){
insertatbegin(12);
insertatbegin(22);
insertatbegin(30);
insertatbegin(44);
insertatbegin(50);
cout << "Linked List: ";
// print list
printList();
} Complete Code
#include <iostream>
using namespace std;
struct node {
int data;
struct node *next;
};
struct node *head = NULL;
struct node *current = NULL;
// display the list
void printList(){
struct node *p = head;
cout << "\n[";
//start from the beginning
while(p != NULL) {
cout << " " << p->data << " ";
p = p->next;
}
cout << "]";
}
//insertion at the beginning
void insertatbegin(int data){
//create a link
struct node *lk = (struct node*) malloc(sizeof(struct node));
lk->data = data;
// point it to old first node
lk->next = head;
//point first to new first node
head = lk;
}
void insertatend(int data){
//create a link
struct node *lk = (struct node*) malloc(sizeof(struct node));
lk->data = data;
struct node *linkedlist = head;
// point it to old first node
while(linkedlist->next != NULL)
linkedlist = linkedlist->next;
//point first to new first node
linkedlist->next = lk;
}
void insertafternode(struct node *list, int data){
struct node *lk = (struct node*) malloc(sizeof(struct node));
lk->data = data;
lk->next = list->next;
list->next = lk;
}
void deleteatbegin(){
head = head->next;
}
void deleteatend(){
struct node *linkedlist = head;
while (linkedlist->next->next != NULL)
linkedlist = linkedlist->next;
linkedlist->next = NULL;
}
void deletenode(int key){
struct node *temp = head, *prev;
if (temp != NULL && temp->data == key) {
head = temp->next;
return;
}
// Find the key to be deleted
while (temp != NULL && temp->data != key) {
prev = temp;
temp = temp->next;
}
// If the key is not present
if (temp == NULL) return;
// Remove the node
prev->next = temp->next;
}
int searchlist(int key){
struct node *temp = head;
while(temp != NULL) {
if (temp->data == key) {
temp=temp->next;
return 1;
} else
return 0;
}
}
int main(){
int k=0;
insertatbegin(12);
insertatbegin(22);
insertatend(30);
insertatend(44);
insertatbegin(50);
insertafternode(head->next->next, 33);
cout << "Linked List: ";
// print list
printList();
deleteatbegin();
deleteatend();
deletenode(12);
cout << "\nLinked List after deletion: ";
// print list
printList();
insertatbegin(4);
insertatbegin(16);
cout << "\nUpdated Linked List: ";
printList();
k = searchlist(16);
if (k == 1)
cout << "\nElement is found";
else
cout << "\nElement is not present in the list";
return 0;
}I hope you liked my article and understood the Singly Link List data structure properly. For more know contact us. And also check Salman Travo Blog for travel blogs. or Check out Queue Data Structure using Array and Stack Data Structure using Array.
