Given two Linked Lists, find the first common element between given linked list i.e., we need to find first node of the first list which is also present in the second list.
Examples:
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 the first list and for every node, we search it in the second list. As soon as we find an element in the second list, we return it.
C++
// 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 codeint 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;} |
Java
// Java program to find first common element // in two unsorted linked listimport java.util.*;class GFG {/* Link list node */static class Node { int data; Node next;};/* A utility function to insert a node at the beginning of a linked list*/static Node push(Node head_ref, int new_data){ Node new_node = new Node(); new_node.data = new_data; new_node.next = head_ref; head_ref = new_node; return head_ref;}/* Returns the first repeating element in linked list*/static int firstCommon(Node head1, 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 codepublic static void main(String[] args){ Node head1 = null; head1 = push(head1, 20); head1 = push(head1, 5); head1 = push(head1, 15); head1 = push(head1, 10); Node head2 = null; head2 = push(head2, 10); head2 = push(head2, 2); head2 = push(head2, 15); head2 = push(head2, 8); System.out.println(firstCommon(head1, head2));}} // This code is contributed by 29AjayKumar |
Python3
# Python3 program to find first common element # in two unsorted linked listimport math# Link list node class Node: def __init__(self, data): self.data = data self.next = None# A utility function to insert a node at the #beginning of a linked listdef push(head_ref, new_data): new_node = Node(new_data) new_node.data = new_data new_node.next = head_ref head_ref = new_node return head_ref# Returns the first repeating element# in linked list*/def firstCommon(head1, head2): # Traverse through every node of first list while(head1 != None): p = head2 # If current node is present in second list while(p != None): if (p.data == head1.data): return head1.data p = p.next head1 = head1.next # If no common node return 0# Driver codeif __name__=='__main__': head1 = None head1 = push(head1, 20) head1 = push(head1, 5) head1 = push(head1, 15) head1 = push(head1, 10) head2 = None head2 = push(head2, 10) head2 = push(head2, 2) head2 = push(head2, 15) head2 = push(head2, 8) print(firstCommon(head1, head2))# This code is contributed by Srathore |
C#
// C# program to find first common element // in two unsorted linked listusing System;using System.Collections.Generic; class GFG {/* Link list node */class Node { public int data; public Node next;};/* A utility function to insert a node at the beginning of a linked list*/static Node push(Node head_ref, int new_data){ Node new_node = new Node(); new_node.data = new_data; new_node.next = head_ref; head_ref = new_node; return head_ref;}/* Returns the first repeating elementin linked list*/static int firstCommon(Node head1, 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 codepublic static void Main(String[] args){ Node head1 = null; head1 = push(head1, 20); head1 = push(head1, 5); head1 = push(head1, 15); head1 = push(head1, 10); Node head2 = null; head2 = push(head2, 10); head2 = push(head2, 2); head2 = push(head2, 15); head2 = push(head2, 8); Console.WriteLine(firstCommon(head1, head2));}} // This code is contributed by PrinciRaj1992 |
Javascript
<script>// Javascript program to find first common element // in two unsorted linked list /* Link list node */class Node { constructor() { this.data = 0; this.next = null; }};/* A utility function to insert a node at the beginning of a linked list*/function push(head_ref, new_data){ var new_node = new Node(); new_node.data = new_data; new_node.next = head_ref; head_ref = new_node; return head_ref;}/* Returns the first repeating elementin linked list*/function firstCommon(head1, head2){ // Traverse through every node of first list for (; head1 != null; head1 = head1.next) // If current node is present in second list for (var p = head2; p != null; p = p.next) if (p.data == head1.data) return head1.data; // If no common node return 0;}// Driver codevar head1 = null;head1 = push(head1, 20);head1 = push(head1, 5);head1 = push(head1, 15);head1 = push(head1, 10);var head2 = null;head2 = push(head2, 10);head2 = push(head2, 2);head2 = push(head2, 15);head2 = push(head2, 8);document.write(firstCommon(head1, head2));</script> |
Output:
10
Time complexity: O(M*N) where M and N are size of given linked lists
Auxiliary Space: O(1)
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