C Exercises: Insert a new node at the middle of the Linked List
Last update on December 20 2021 09:10:19 [UTC/GMT +8 hours]Required knowledge
Basic C programming, Functions, Singly linked list, Dynamic memory allocation
Algorithm to insert node at the middle of singly Linked List
Linked List | Set 2 [Inserting a node]
We have introduced Linked Lists in the previous post. We also created a simple linked list with 3 nodes and discussed linked list traversal.
All programs discussed in this post consider the following representations of linked list.
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// A linked list node
class Node
{
public:
int data;
Node *next;
};
// This code is contributed by rathbhupendra
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// A linked list node
struct Node
{
int data;
struct Node *next;
};
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// Linked List Class
class LinkedList
{
Node head; // head of list
/* Node Class */
class Node
{
int data;
Node next;
// Constructor to create a new node
Node[int d] {data = d; next = null; }
}
}
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# Node class
class Node:
# Function to initialize the node object
def __init__[self, data]:
self.data = data # Assign data
self.next = None # Initialize next as null
# Linked List class
class LinkedList:
# Function to initialize the Linked List object
def __init__[self]:
self.head = None
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/* Linked list Node*/
public class Node
{
public int data;
public Node next;
public Node[int d] {data = d; next = null; }
}
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// Linked List Class
var head; // head of list
/* Node Class */
class Node {
// Constructor to create a new node
constructor[d] {
this.data = d;
this.next = null;
}
}
// This code is contributed by todaysgaurav
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In this post, methods to insert a new node in linked list are discussed. A node can be added in three ways
1] At the front of the linked list
2] After a given node.
3] At the end of the linked list.
C Program For Inserting A Node In A Linked List
We have introduced Linked Lists in the previous post. We also created a simple linked list with 3 nodes and discussed linked list traversal.
All programs discussed in this post consider the following representations of the linked list.
|
// A linked list node
struct Node
{
int data;
struct Node *next;
};
|
In this post, methods to insert a new node in linked list are discussed. A node can be added in three ways
1] At the front of the linked list
2] After a given node.
3] At the end of the linked list.
Add a node at the front: [4 steps process]
The new node is always added before the head of the given Linked List. And newly added node becomes the new head of the Linked List. For example, if the given Linked List is 10->15->20->25 and we add an item 5 at the front, then the Linked List becomes 5->10->15->20->25. Let us call the function that adds at the front of the list is push[]. The push[] must receive a pointer to the head pointer, because push must change the head pointer to point to the new node [See this]
Following are the 4 steps to add a node at the front.
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// Given a reference [pointer to pointer] to
// the head of a list and an int, inserts a
// new node on the front of the list.
void push[struct Node** head_ref,
int new_data]
{
// 1. Allocate node
struct Node* new_node =
[struct Node*] malloc[sizeof[struct Node]];
// 2. put in the data
new_node->data = new_data;
// 3. Make next of new node as head
new_node->next = [*head_ref];
// 4. move the head to point to
// the new node
[*head_ref] = new_node;
}
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Time complexity of push[] is O[1] as it does a constant amount of work.
Add a node after a given node: [5 steps process]
We are given a pointer to a node, and the new node is inserted after the given node.
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// Given a node prev_node, insert a
// new node after the given prev_node
void insertAfter[struct Node* prev_node,
int new_data]
{
// 1. Check if the given prev_node
// is NULL
if [prev_node == NULL]
{
printf["the given previous node cannot be NULL"];
return;
}
// 2. Allocate new node
struct Node* new_node =
[struct Node*] malloc[sizeof[struct Node]];
// 3. Put in the data
new_node->data = new_data;
// 4. Make next of new node as next
// of prev_node
new_node->next = prev_node->next;
// 5. Move the next of prev_node
// as new_node
prev_node->next = new_node;
}
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Time complexity of insertAfter[] is O[1] as it does a constant amount of work.
Add a node at the end: [6 steps process]
The new node is always added after the last node of the given Linked List. For example if the given Linked List is 5->10->15->20->25 and we add an item 30 at the end, then the Linked List becomes 5->10->15->20->25->30.
Since a Linked List is typically represented by the head of it, we have to traverse the list till the end and then change the next to last node to a new node.
Following are the 6 steps to add node at the end.
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// Given a reference [pointer to pointer] to
// the head of a list and an int, appends a
// new node at the end
void append[struct Node** head_ref,
int new_data]
{
// 1. Allocate node
struct Node* new_node =
[struct Node*] malloc[sizeof[struct Node]];
// Used in step 5
struct Node *last = *head_ref;
// 2. Put in the data
new_node->data = new_data;
// 3. This new node is going to be the
// last node, so make next of it as NULL
new_node->next = NULL;
// 4. If the Linked List is empty, then make
// the new node as head
if [*head_ref == NULL]
{
*head_ref = new_node;
return;
}
// 5. Else traverse till the last node
while [last->next != NULL]
last = last->next;
// 6. Change the next of last node
last->next = new_node;
return;
}
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Time complexity of append is O[n] where n is the number of nodes in the linked list. Since there is a loop from head to end, the function does O[n] work.
This method can also be optimized to work in O[1] by keeping an extra pointer to the tail of the linked list.
Following is a complete program that uses all of the above methods to create a linked list.
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// A complete working C program to demonstrate
// all insertion methods on Linked List
#include
#include
// A linked list node
struct Node
{
int data;
struct Node *next;
};
// Given a reference [pointer to pointer] to
// the head of a list and an int, inserts a
// new node on the front of the list.
void push[struct Node** head_ref,
int new_data]
{
// 1. Allocate node
struct Node* new_node =
[struct Node*] malloc[sizeof[struct Node]];
// 2. Put in the data
new_node->data = new_data;
// 3. Make next of new node as head
new_node->next = [*head_ref];
// 4. move the head to point to
// the new node
[*head_ref] = new_node;
}
// Given a node prev_node, insert a
// new node after the given prev_node
void insertAfter[struct Node* prev_node,
int new_data]
{
// 1. Check if the given prev_node
// is NULL
if [prev_node == NULL]
{
printf["the given previous node cannot be NULL"];
return;
}
// 2. Allocate new node
struct Node* new_node =
[struct Node*] malloc[sizeof[struct Node]];
// 3. Put in the data
new_node->data = new_data;
// 4. Make next of new node as next
// of prev_node
new_node->next = prev_node->next;
// 5. Move the next of prev_node
// as new_node
prev_node->next = new_node;
}
// Given a reference [pointer to pointer] to
// the head of a list and an int, appends a
// new node at the end
void append[struct Node** head_ref,
int new_data]
{
// 1. Allocate node
struct Node* new_node =
[struct Node*] malloc[sizeof[struct Node]];
// Used in step 5
struct Node *last = *head_ref;
// 2. Put in the data
new_node->data = new_data;
// 3. This new node is going to be the
// last node, so make next of it as NULL
new_node->next = NULL;
// 4. If the Linked List is empty, then make
// the new node as head
if [*head_ref == NULL]
{
*head_ref = new_node;
return;
}
// 5. Else traverse till the last node
while [last->next != NULL]
last = last->next;
// 6. Change the next of last node
last->next = new_node;
return;
}
// This function prints contents of the
// linked list starting from head
void printList[struct Node *node]
{
while [node != NULL]
{
printf[" %d ", node->data];
node = node->next;
}
}
// Driver code
int main[]
{
// Start with the empty list
struct Node* head = NULL;
// Insert 6. So linked list
// becomes 6->NULL
append[&head, 6];
// Insert 7 at the beginning.
// So linked list becomes 7->6->NULL
push[&head, 7];
// Insert 1 at the beginning. So
// linked list becomes 1->7->6->NULL
push[&head, 1];
// Insert 4 at the end. So linked list
// becomes 1->7->6->4->NULL
append[&head, 4];
// Insert 8, after 7. So linked list
// becomes 1->7->8->6->4->NULL
insertAfter[head->next, 8];
printf["Created Linked list is: "];
printList[head];
return 0;
}
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Output:
Created Linked list is: 1 7 8 6 4Please refer complete article on Linked List | Set 2 [Inserting a node] for more details!
inserting a node at the end of a linked list
The new node will be added at the end of the linked list.
Inserting a node at the beginning of a linked list
The new node will be added at the beginning of a linked list.
Example
Assume that the linked list has elements: 20 30 40 NULL
If we insert 100, it will be added at the beginning of a linked list.
After insertion, the new linked list will be
100 20 30 40 NULL
Program to insert a new node at the middle of the singly linked list
Explanation
In this program, we will create a singly linked list and add a new node at the middle of the list. To accomplish this task, we will calculate the size of the list and divide it by 2 to get the mid-point of the list where the new node needs to be inserted.
Consider the above diagram; node 1 represents the head of the original list. Let node New is the new node which needs to be added at the middle of the list. First, we calculate size which in this case is 4. So, to get the mid-point, we divide it by 2 and store it in a variable count. Node current will point to head. First, we iterate through the list till current points to mid position. Define another node temp which point to node next to current. Insert the New node between current and temp.
Algorithm
- Create a class Node which has two attributes: data and next. Next is a pointer to the next node in the list.
- Create another class InsertMid which has three attributes: head, tail, and size that keep tracks of a number of nodes present in the list.
- addNode[] will add a new node to the list:
- Create a new node.
- It first checks, whether the head is equal to null which means the list is empty.
- If the list is empty, both head and tail will point to a newly added node.
- If the list is not empty, the new node will be added to end of the list such that tail's next will point to a newly added node. This new node will become the new tail of the list.
- addInMid[] will add a new node at the middle of the list:
- It first checks, whether the head is equal to null which means the list is empty.
- If the list is empty, both head and tail will point to a newly added node.
- If the list is not empty, then calculate the size of the list and divide it by 2 to get mid-point of the list.
- Define node current that will iterate through the list till current will point to mid node.
- Define another node temp which will point to node next to current.
- The new node will be inserted after current and before temp such that current will point to the new node and the new node will point to temp.
- display[] will display the nodes present in the list:
- Define a node current which will initially point to the head of the list.
- Traverse through the list till current points to null.
- Display each node by making current to point to node next to it in each iteration.
Solution
Python
Output:
C
Output:
JAVA
Output:
C#
Output:
PHP
Output:
Linked List Operations: Traverse, Insert and Delete
In this tutorial, you will learn different operations on a linked list. Also, you will find implementation of linked list operations in C/C++, Python and Java.
There are various linked list operations that allow us to perform different actions on linked lists. For example, the insertion operation adds a new element to the linked list.
Here's a list of basic linked list operations that we will cover in this article.
- Traversal - access each element of the linked list
- Insertion - adds a new element to the linked list
- Deletion - removes the existing elements
- Search - find a node in the linked list
- Sort - sort the nodes of the linked list
Before you learn about linked list operations in detail, make sure to know about Linked List first.
Things to Remember about Linked List
- head points to the first node of the linked list
- next pointer of the last node is NULL, so if the next current node is NULL, we have reached the end of the linked list.
In all of the examples, we will assume that the linked list has three nodes 1 --->2 --->3 with node structure as below:
struct node { int data; struct node *next; };