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Write a function to get the intersection point of two Linked Lists | Set 2
• Difficulty Level : Medium
• Last Updated : 09 Jun, 2021

There are two singly linked lists in a system. By some programming error, the end node of one of the linked list got linked to the second list, forming an inverted Y shaped list. Write a program to get the point where two linked list merge. Above diagram shows an example with two linked list having 15 as intersection point.

Approach: It can be observed that the number of nodes in traversing the first linked list and then from the head of the second linked list to intersection point is equal to the number of nodes involved in traversing the second linked list and then from head of the first list to the intersection point. Considering the example given above, start traversing the two linked lists with two pointers curr1 and curr2 pointing to the heads of the given linked lists respectively.

1. If curr1 != null then update it to point to the next node, else it is updated to point to the first node of the second list.
2. If curr2 != null then update it to point to the next node, else it is updated to point to the first node of the first list.
3. Repeat the above steps while curr1 is not equal to curr2.

The two pointers curr1 and curr2 will be pointing to the same node now i.e. the merging point.
Below is the implementation of the above approach:

## C++

 `// C++ implementation of the approach``#include ``using` `namespace` `std;` `// Link list node``struct` `Node {``    ``int` `data;``    ``Node* next;``};` `// Function to get the intersection point``// of the given linked lists``int` `getIntersectionNode(Node* head1, Node* head2)``{``    ``Node *curr1 = head1, *curr2 = head2;` `    ``// While both the pointers are not equal``    ``while` `(curr1 != curr2) {` `        ``// If the first pointer is null then``        ``// set it to point to the head of``        ``// the second linked list``        ``if` `(curr1 == NULL) {``            ``curr1 = head2;``        ``}` `        ``// Else point it to the next node``        ``else` `{``            ``curr1 = curr1->next;``        ``}` `        ``// If the second pointer is null then``        ``// set it to point to the head of``        ``// the first linked list``        ``if` `(curr2 == NULL) {``            ``curr2 = head1;``        ``}` `        ``// Else point it to the next node``        ``else` `{``            ``curr2 = curr2->next;``        ``}``    ``}` `    ``// Return the intersection node``    ``return` `curr1->data;``}` `// Driver code``int` `main()``{``    ``/*``    ``Create two linked lists` `    ``1st Linked list is 3->6->9->15->30``    ``2nd Linked list is 10->15->30``    ` `    ``15 is the intersection point``    ``*/` `    ``Node* newNode;``    ``Node* head1 = ``new` `Node();``    ``head1->data = 10;``    ``Node* head2 = ``new` `Node();``    ``head2->data = 3;``    ``newNode = ``new` `Node();``    ``newNode->data = 6;``    ``head2->next = newNode;``    ``newNode = ``new` `Node();``    ``newNode->data = 9;``    ``head2->next->next = newNode;``    ``newNode = ``new` `Node();``    ``newNode->data = 15;``    ``head1->next = newNode;``    ``head2->next->next->next = newNode;``    ``newNode = ``new` `Node();``    ``newNode->data = 30;``    ``head1->next->next = newNode;``    ``head1->next->next->next = NULL;` `    ``// Print the intersection node``    ``cout << getIntersectionNode(head1, head2);` `    ``return` `0;``}`

## Java

 `// Java implementation of the approach``class` `GFG``{` `// Link list node``static` `class` `Node``{``    ``int` `data;``    ``Node next;``};` `// Function to get the intersection point``// of the given linked lists``static` `int` `getIntersectionNode(Node head1, Node head2)``{``    ``Node curr1 = head1, curr2 = head2;` `    ``// While both the pointers are not equal``    ``while` `(curr1 != curr2)``    ``{` `        ``// If the first pointer is null then``        ``// set it to point to the head of``        ``// the second linked list``        ``if` `(curr1 == ``null``)``        ``{``            ``curr1 = head2;``        ``}` `        ``// Else point it to the next node``        ``else``        ``{``            ``curr1 = curr1.next;``        ``}` `        ``// If the second pointer is null then``        ``// set it to point to the head of``        ``// the first linked list``        ``if` `(curr2 == ``null``)``        ``{``            ``curr2 = head1;``        ``}` `        ``// Else point it to the next node``        ``else``        ``{``            ``curr2 = curr2.next;``        ``}``    ``}` `    ``// Return the intersection node``    ``return` `curr1.data;``}` `// Driver code``public` `static` `void` `main(String[] args)``{``    ``/*``    ``Create two linked lists` `    ``1st Linked list is 3.6.9.15.30``    ``2nd Linked list is 10.15.30``    ` `    ``15 is the intersection point``    ``*/` `    ``Node newNode;``    ``Node head1 = ``new` `Node();``    ``head1.data = ``10``;``    ``Node head2 = ``new` `Node();``    ``head2.data = ``3``;``    ``newNode = ``new` `Node();``    ``newNode.data = ``6``;``    ``head2.next = newNode;``    ``newNode = ``new` `Node();``    ``newNode.data = ``9``;``    ``head2.next.next = newNode;``    ``newNode = ``new` `Node();``    ``newNode.data = ``15``;``    ``head1.next = newNode;``    ``head2.next.next.next = newNode;``    ``newNode = ``new` `Node();``    ``newNode.data = ``30``;``    ``head1.next.next = newNode;``    ``head1.next.next.next = ``null``;` `    ``// Print the intersection node``    ``System.out.print(getIntersectionNode(head1, head2));``}``}` `// This code is contributed by 29AjayKumar`

## Python3

 `# Python3 implementation of the approach` `# Link list node``class` `Node:``    ``def` `__init__(``self``):``        ``self``.data ``=` `0``        ``self``.``next` `=` `None` `# Function to get the intersection point``# of the given linked lists``def` `getIntersectionNode( head1, head2):` `    ``curr1 ``=` `head1``    ``curr2 ``=` `head2` `    ``# While both the pointers are not equal``    ``while` `(curr1 !``=` `curr2):` `        ``# If the first pointer is None then``        ``# set it to point to the head of``        ``# the second linked list``        ``if` `(curr1 ``=``=` `None``) :``            ``curr1 ``=` `head2``        ` `        ``# Else point it to the next node``        ``else``:``            ``curr1 ``=` `curr1.``next``        ` `        ``# If the second pointer is None then``        ``# set it to point to the head of``        ``# the first linked list``        ``if` `(curr2 ``=``=` `None``):``            ``curr2 ``=` `head1``        ` `        ``# Else point it to the next node``        ``else``:``            ``curr2 ``=` `curr2.``next``        ` `    ``# Return the intersection node``    ``return` `curr1.data` `# Driver code` `# Create two linked lists` `# 1st Linked list is 3.6.9.15.30``# 2nd Linked list is 10.15.30``    ` `# 15 is the intersection point` `newNode ``=` `None``head1 ``=` `Node()``head1.data ``=` `10``head2 ``=` `Node()``head2.data ``=` `3``newNode ``=` `Node()``newNode.data ``=` `6``head2.``next` `=` `newNode``newNode ``=` `Node()``newNode.data ``=` `9``head2.``next``.``next` `=` `newNode``newNode ``=` `Node()``newNode.data ``=` `15``head1.``next` `=` `newNode``head2.``next``.``next``.``next` `=` `newNode``newNode ``=` `Node()``newNode.data ``=` `30``head1.``next``.``next` `=` `newNode``head1.``next``.``next``.``next` `=` `None` `# Print the intersection node``print``( getIntersectionNode(head1, head2))` `# This code is contributed by Arnab Kundu`

## C#

 `// C# implementation of the approach``using` `System;` `class` `GFG``{` `// Link list node``public` `class` `Node``{``    ``public` `int` `data;``    ``public` `Node next;``};` `// Function to get the intersection point``// of the given linked lists``static` `int` `getIntersectionNode(Node head1,``                               ``Node head2)``{``    ``Node curr1 = head1, curr2 = head2;` `    ``// While both the pointers are not equal``    ``while` `(curr1 != curr2)``    ``{` `        ``// If the first pointer is null then``        ``// set it to point to the head of``        ``// the second linked list``        ``if` `(curr1 == ``null``)``        ``{``            ``curr1 = head2;``        ``}` `        ``// Else point it to the next node``        ``else``        ``{``            ``curr1 = curr1.next;``        ``}` `        ``// If the second pointer is null then``        ``// set it to point to the head of``        ``// the first linked list``        ``if` `(curr2 == ``null``)``        ``{``            ``curr2 = head1;``        ``}` `        ``// Else point it to the next node``        ``else``        ``{``            ``curr2 = curr2.next;``        ``}``    ``}` `    ``// Return the intersection node``    ``return` `curr1.data;``}` `// Driver code``public` `static` `void` `Main(String[] args)``{``    ``/*``    ``Create two linked lists` `    ``1st Linked list is 3.6.9.15.30``    ``2nd Linked list is 10.15.30``    ` `    ``15 is the intersection point``    ``*/``    ``Node newNode;``    ``Node head1 = ``new` `Node();``    ``head1.data = 10;``    ``Node head2 = ``new` `Node();``    ``head2.data = 3;``    ``newNode = ``new` `Node();``    ``newNode.data = 6;``    ``head2.next = newNode;``    ``newNode = ``new` `Node();``    ``newNode.data = 9;``    ``head2.next.next = newNode;``    ``newNode = ``new` `Node();``    ``newNode.data = 15;``    ``head1.next = newNode;``    ``head2.next.next.next = newNode;``    ``newNode = ``new` `Node();``    ``newNode.data = 30;``    ``head1.next.next = newNode;``    ``head1.next.next.next = ``null``;` `    ``// Print the intersection node``    ``Console.Write(getIntersectionNode(head1, head2));``}``}` `// This code is contributed by Rajput-Ji`

## Javascript

 ``
Output:
`15`

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