# Print all triplets with sum S in given sorted Linked List

• Difficulty Level : Medium
• Last Updated : 13 Dec, 2021

Given a sorted singly linked list as list of N distinct nodes (no two nodes have the same data) and an integer S. The task is to find all distinct triplets in the list that sum up to given integer S.

Examples:

Input: list = 1->2->4->5->6->8->9,  S = 15
Output: [(1, 5, 9), (1, 6, 8), (2, 4, 9), (2 ,5, 8), (4, 5, 6)]
Explanation: These are the only distinct triplets which have sum equal to S i.e 15. Note that (2, 4, 9) and (9, 4, 2) both triplets have sum 15 but they are not distinct as all the elements of the triplets are same.

Input: list = 1->2->4->5->6->8->9,  S = 17
Output: [(2, 6, 9), (4, 5, 8)]

Naive approach: Use three nested loop. Generate all triplets and find the distinct triplets having sum equal to S.
Time Complexity: O(N3)
Auxiliary Space: O(N3)

Efficient Approach: Use concept of hashing to efficiently solve the problem. Follow the steps mentioned below

1. Create a hash array to store the scanned node data.
2. Insert head node value into the hash array.
3. Now start traversing the linked list using nested loops, and in each iteration:
• Subtract the data of both the nodes from the given integer ‘S’ to find the value which makes the triplet.
• Now find that value in the hash array.
• If that value is present in the hash array(i. e. triplet is found), then store the triplet in a list as a possible answer.
4. Return the list.

Below is the implementation of the above approach:

## C++

 `// C++ code to find``// all distinct triplets having sum S``#include ``using` `namespace` `std;` `// Structure of node of singly linked list``struct` `Node {``    ``int` `data;``    ``Node* next;``    ``Node(``int` `x)``    ``{``        ``data = x;``        ``next = NULL;``    ``}``};` `// Inserting new node``// at the  beginning of the linked list``void` `push(``struct` `Node** head_ref,``          ``int` `new_data)``{``    ``// Create a new node with the given data.``    ``struct` `Node* new_node``      ``= ``new` `Node(new_data);``    ` `    ``// Make the new node point to the head.``    ``new_node->next = (*head_ref);``    ` `    ``// Make the new node as the head node.``    ``(*head_ref) = new_node;``}` `// Function to print triplets``// in a sorted singly linked list``// whose sum is equal to given value 'S'``vector>``  ``printTriplets(``struct` `Node* head, ``int` `S)``{``    ``// Declare unordered map``    ``// to store the scanned value``    ``unordered_map<``int``, ``bool``> mp;``    ` `    ``// Vector to store the triplets``    ``vector> v;` `    ``// Declare two pointers 'p' and 'q'``    ``// for traversing singly linked list``    ``struct` `Node* p;``    ``struct` `Node* q;` `    ``// Insert 1st node data into map``    ``// and start traversing from next node``    ``mp[head->data] = ``true``;` `    ``// Outer loop terminates``    ``// when last node reached``    ``for` `(p = head->next; p->next != NULL;``         ``p = p->next) {` `        ``// Inner loop terminates``        ``// when second pointer become NULL``        ``for` `(q = p->next; q != NULL;``             ``q = q->next) {` `            ``// Temporary vector``            ``// to store the current triplet``            ``vector<``int``> temp;``            ``int` `second = p->data;``            ``int` `third = q->data;` `            ``// find the number required``            ``// to make triplet by subtracting``            ``// node1 and node2 data from S``            ``// and store it.``            ``int` `first = S - second - third;` `            ``// Search if that value``            ``// is present in the map or not``            ``if` `(mp.find(first)``                ``!= mp.end()) {` `                ``// If 'first' is present``                ``// in map, make a triplet of``                ``// first,second & third``                ``temp.push_back(mp.find(first)->first);``                ``temp.push_back(second);``                ``temp.push_back(third);` `                ``// Push current triplet``                ``// stored in 'temp' to``                ``// vector 'v'``                ``v.push_back(temp);``            ``}``        ``}``        ` `        ``// Insert current node data into map``        ``mp[p->data] = ``true``;``    ``}``    ` `    ``// Return a vector of triplets.``    ``return` `v;``}` `// Driver code``int` `main()``{``    ``int` `S = 15;``    ` `    ``// Create an empty singly linked list``    ``struct` `Node* head = NULL;``    ``vector > ans;` `    ``// Insert values in sorted order``    ``push(&head, 9);``    ``push(&head, 8);``    ``push(&head, 6);``    ``push(&head, 5);``    ``push(&head, 4);``    ``push(&head, 2);``    ``push(&head, 1);``    ` `    ``// Call printTriplets function``    ``// to find all triplets in``    ``// the linked list``    ``ans = printTriplets(head, S);` `    ``// Sort and  display``    ``// all possible triplets``    ``sort(ans.begin(), ans.end());``    ``for` `(``int` `i = 0; i < ans.size(); i++) {``        ``for` `(``int` `j = 0;``             ``j < ans[i].size(); j++) {``            ``cout << ans[i][j] << ``" "``;``        ``}``        ``cout << ``"\n"``;``    ``}``    ``return` `0;``}`

## Java

 `// Java code to find``// all distinct triplets having sum S``import` `java.util.ArrayList;``import` `java.util.Collections;``import` `java.util.Comparator;``import` `java.util.HashMap;` `class` `GFG``{``  ` `    ``// Structure of node of singly linked list``    ``static` `class` `Node {``        ``int` `data;``        ``Node next;` `        ``public` `Node(``int` `x) {``            ``data = x;``            ``next = ``null``;``        ``}``    ``};` `    ``// Function to print triplets``    ``// in a sorted singly linked list``    ``// whose sum is equal to given value 'S'``    ``public` `static` `ArrayList> printTriplets(Node head, ``int` `S) {``        ``// Declare unordered map``        ``// to store the scanned value``        ``HashMap mp = ``new` `HashMap();` `        ``// Vector to store the triplets``        ``ArrayList> v = ``new` `ArrayList>();` `        ``// Declare two pointers 'p' and 'q'``        ``// for traversing singly linked list``        ``Node p;``        ``Node q;` `        ``// Insert 1st node data into map``        ``// and start traversing from next node``        ``mp.put(head.data, ``true``);` `        ``// Outer loop terminates``        ``// when last node reached``        ``for` `(p = head.next; p.next != ``null``; p = p.next) {` `            ``// Inner loop terminates``            ``// when second pointer become null``            ``for` `(q = p.next; q != ``null``; q = q.next) {` `                ``// Temporary vector``                ``// to store the current triplet``                ``ArrayList temp = ``new` `ArrayList();``                ``int` `second = p.data;``                ``int` `third = q.data;` `                ``// find the number required``                ``// to make triplet by subtracting``                ``// node1 and node2 data from S``                ``// and store it.``                ``int` `first = S - second - third;` `                ``// Search if that value``                ``// is present in the map or not``                ``if` `(mp.containsKey(first)) {` `                    ``// If 'first' is present``                    ``// in map, make a triplet of``                    ``// first,second & third``                    ``temp.add(first);``                    ``temp.add(second);``                    ``temp.add(third);` `                    ``// Push current triplet``                    ``// stored in 'temp' to``                    ``// vector 'v'``                    ``v.add(temp);``                ``}``            ``}` `            ``// Insert current node data into map``            ``mp.put(p.data, ``true``);``        ``}` `        ``// Return a vector of triplets.``        ``return` `v;``    ``}` `    ``// Driver code``    ``public` `static` `void` `main(String args[]) {``        ``int` `S = ``15``;` `        ``// Create an empty singly linked list``        ``Node head = ``null``;``        ``ArrayList> ans = ``new` `ArrayList>();` `        ``// Insert values in sorted order``        ``head = ``new` `Node(``9``);``        ``head.next = ``new` `Node(``8``);``        ``head.next.next = ``new` `Node(``6``);``        ``head.next.next.next = ``new` `Node(``5``);``        ``head.next.next.next.next = ``new` `Node(``4``);``        ``head.next.next.next.next.next = ``new` `Node(``2``);``        ``head.next.next.next.next.next.next = ``new` `Node(``1``);` `        ``// Call printTriplets function``        ``// to find all triplets in``        ``// the linked list``        ``ans = printTriplets(head, S);` `        ``// Sort and display``        ``// all possible triplets``        ``for` `(ArrayList x : ans) {``            ``Collections.sort(x);``        ``}` `        ``Collections.sort(ans, ``new` `Comparator>() {``            ``@Override``            ``public` `int` `compare(ArrayList o1, ArrayList o2) {``                ``return` `o2.get(``0``) - (o1.get(``0``));``            ``}``        ``});``        ``Collections.reverse(ans);` `        ``for` `(``int` `i = ``0``; i < ans.size(); i++) {``            ``for` `(``int` `j = ``0``; j < ans.get(i).size(); j++) {``                ``System.out.print(ans.get(i).get(j) + ``" "``);``            ``}``            ``System.out.println(``""``);``        ``}``    ``}``}` `// This code is contributed by gfgking.`

## Javascript

 ``

Output
```1 5 9
1 6 8
2 4 9
2 5 8
4 5 6 ```

Time Complexity: O(N2)
Auxiliary Space: O(N)

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