First common element in two linked lists

Given two Linked Lists, find the first common element between given linked list i.e., we need to find first node of first list which is also present in second list.

Input :  
   List1: 10->15->4->20
   Lsit2:  8->4->2->10
Output : 10

Input : 
   List1: 1->2->3->4
   Lsit2:  5->6->3->8
Output : 3

We traverse first list and for every node, we search it in second list. As soon as we find an element in second list, we return it.





// C++ program to find first common element in
// two unsorted linked list
#include <bits/stdc++.h>
using namespace std;
/* Link list node */
struct Node {
    int data;
    struct Node* next;
/* A utility function to insert a node at the 
   beginning of a linked list*/
void push(struct Node** head_ref, int new_data)
    struct Node* new_node = 
          (struct Node*)malloc(sizeof(struct Node));
    new_node->data = new_data;
    new_node->next = (*head_ref);
    (*head_ref) = new_node;
/* Returns the first repeating element in linked list*/
int firstCommon(struct Node* head1, struct Node* head2)
    // Traverse through every node of first list
    for (; head1 != NULL; head1=head1->next)
       // If current node is present in second list
       for (Node *p = head2; p != NULL; p = p->next)
            if (p->data == head1->data)
                return head1->data;
    // If no common node
    return 0;
// Driver code
int main()
    struct Node* head1 = NULL;
    push(&head1, 20);
    push(&head1, 5);
    push(&head1, 15);
    push(&head1, 10);
    struct Node* head2 = NULL;
    push(&head2, 10);
    push(&head2, 2);
    push(&head2, 15);
    push(&head2, 8);
    cout << firstCommon(head1, head2);
    return 0;




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