C Program to Find the First Common Element in Two Linked Lists

This C Program finds the first common element between the 2 given linked list.

Here is a source code of the C Program to find the first common element between the 2 given linked list. The C program is successfully compiled and run on a Linux system. The program output is also shown below.

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/*
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 * C Program to Find the first Common Element between the 2 given Linked Lists

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 */
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#include <stdio.h>
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#include <stdlib.h>
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struct node
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{
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    int num;
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    struct node *next;
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};
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void create(struct node **);
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int find(struct node *, struct node *);
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void release(struct node **);
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void display(struct node *);
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int main()
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{
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    struct node *p = NULL, *q = NULL;
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    int result;
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    printf("Enter data into the list\n");

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    create(&p);
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    printf("Enter data into the list\n");

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    create(&q);
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    printf("Displaying list1:\n");
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    display(p);
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    printf("Displaying list2:\n");
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    display(q);
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    result = find(p, q);
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    if (result)
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    {
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        printf("The first matched element is %d.\n", result);

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    }
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    else
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    {
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        printf("No matching element found.\n");

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    }
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    release (&p);
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    return 0;
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}
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```
 
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int find(struct node *p, struct node *q)

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{
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    struct node *temp;
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    while (p != NULL)
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    {
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        temp = q;
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        while (temp != NULL)
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        {
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            if (temp->num == p->num)
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            {
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                return p->num;
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            }
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            temp = temp->next;
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        }
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        p = p->next;
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    }
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    /*Assuming 0 is not used in the list*/

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    return 0;
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}
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```
 
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void create(struct node **head)
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```
{
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    int c, ch;
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    struct node *temp, *rear;
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    do
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    {
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        printf("Enter number: ");
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        scanf("%d", &c);
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        temp = (struct node *)malloc(sizeof(struct node));

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        temp->num = c;
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        temp->next = NULL;
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        if (*head == NULL)
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        {
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            *head = temp;
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        }
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        else
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        {
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            rear->next = temp;
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        }
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        rear = temp;
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        printf("Do you wish to continue [1/0]: ");

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        scanf("%d", &ch);
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    } while (ch != 0);
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    printf("\n");
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}
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```
 
```
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void display(struct node *head)
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```
{
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    while (head != NULL)
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```
    {
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        printf("%d\t", head->num);
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        head = head->next;
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    }
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    printf("\n");
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}
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```
 
```
```
void release(struct node **head)
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{
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    struct node *temp;
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    while ((*head) != NULL)
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```
    {
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        temp = *head;
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        (*head) = (*head)->next;
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        free(temp);
```
```
    }
```
```
}
```

$ cc firstcommon.c 
$ ./a.out
Enter data into the list1
Enter number: 2
Do you wish to continue [1/0]: 1
Enter number: 8
Do you wish to continue [1/0]: 1
Enter number: 5
Do you wish to continue [1/0]: 1
Enter number: 6
Do you wish to continue [1/0]: 0
 
Enter data into the list2
Enter number: 3
Do you wish to continue [1/0]: 1
Enter number: 5
Do you wish to continue [1/0]: 1
Enter number: 9
Do you wish to continue [1/0]: 0
 
Displaying list1:
2	8	5	6	
Displaying list2:
3	5	9	
The first matched element is 5.