DATA STRUCTURES IN C – LINKED LIST (20 PROGRAMS)

Linked List in C- Merge two Linked List into Single Linked List – Efficient :

Input
Linked List 1: one->three->five->seven
Head of Linked List 1 is head1

Linked List 2: two->four->six
Head of Linked List 2 is head2

Output
Linked List 3: one->two->three->four->five->six->seven

Head of Linked List 3 is head1

This program works irrespective of size of the two input linked list.

Source Code :

#include<stdio.h>

	//Input
	//Linked List 1: one->three->five->seven
	//Head of Linked List 1 is head1 
	//
	//Linked List 2: two->four->six
	//Head of Linked List 2 is head2
	//
	//Output
	//Linked List 3: one->two->three->four->five->six->seven
	//Head of Linked List 3 is head1

struct node
{
    	//Structure named node to store integer in variable data and a pointer variable which can store address location of next node
    	int data;
    	struct node *next;
    	//Pointer variable next is a self referential pointer which stores the address of structure node
};

struct node *head1 = NULL;
struct node *head2 = NULL;
//Pointer head1 and head2 are the pointers which stores the address of two input linked list

void merge()
{
    	//Function to merge the two input linked list
    	struct node *temp1 = head1;
    	struct node *temp2 = head2;
    	//Use a new pointer variable temp1 and temp2
    	//Do not use the pointer variable head1 and head2 directly. If we use it, the address location of the first node in the two linked list will be lost

    	struct node *holder1 = NULL;
    	struct node *holder2 = NULL;
    	//Temporary pointer variables to store the address of next node of the two input linked list

    	while(temp1!=NULL && temp2!=NULL)	
    	{
	        	//Executes until both temp1 and temp2 are not NULL

        		holder1=temp1->next;
        		//Storing the address of next node of first linked list

        		temp1->next=temp2;
        		//Making the first node of first linked list point to first node of second linked list

        		if(holder1!=NULL)			
        		{
            			//Making the first node of second linked list point to second node of first linked list
            			holder2=temp2->next;
            			temp2->next=holder1;
		        }							
        		temp1=holder1;
        		temp2=holder2;	
        		//Updating the address location of two pointer variables temp1 and temp2
    	}
}

void print(struct node *temp)
{
    	//This funtion is used to print the data in each of the node in the linked list
    	//Process of moving from one node to another node is called as traversing
    	while(temp!=NULL)
    	{
        		printf("\n%d ",temp->data);
        		temp=temp->next;		
    	}	
}

int main()
{
    	struct node *one = (struct node*)malloc(sizeof(struct node));
    	struct node *two = (struct node*)malloc(sizeof(struct node));
    	struct node *three = (struct node*)malloc(sizeof(struct node));
    	struct node *four = (struct node*)malloc(sizeof(struct node));
    	struct node *five = (struct node*)malloc(sizeof(struct node));
    	struct node *six = (struct node*)malloc(sizeof(struct node));
    	struct node *seven = (struct node*)malloc(sizeof(struct node));
    	//Seven nodes are created

    	head1=one;
    	head2=two;
    	//head1 points to first node of first linked list
    	//head2 points to first node of second linked list

    	one->data=1;
    	one->next=three;

    	two->data=2;	
    	two->next=four;

    	three->data=3;
    	three->next=five;

    	four->data=4;
    	four->next=six;

    	five->data=5;
    	five->next=seven;

    	six->data=6;
    	six->next=NULL;
    	//Last node of second input linked list

    	seven->data=7;
    	seven->next=NULL;
    	//Last node of first input linked list

    	//Input
    	//Linked List 1: one->three->five->seven
    	//Head of Linked List 1 is head1 
    	//
    	//Linked List 2: two->four->six
    	//Head of Linked List 2 is head2
    	//
    	//Output
    	//Linked List 3: one->two->three->four->five->six->seven
	    //Head of Linked List 3 is head1

    	printf("\nBefore Merging");
    	printf("\nInput: Linked List 1");
    	print(head1);

    	printf("\nInput: Linked List 2");
    	print(head2);

    	merge();
    	//Merging the two linked list into single linked list

    	printf("\nAfter Merging");
    	printf("\nOutput: Linked List 3");
    	print(head1);

    	return 0;
}

Output :

Before Merging
Input: Linked List 1
// Head pointer of first linked list is head1
1
3
5
7

Input: Linked List 2
// Head pointer of second linked list is head2
2
4
6

After Merging
Output: Linked List 3
// Head pointer of output linked list is head1
1
2
3
4
5
6
7