Count Triplets in a Sorted Doubly Linked List Whose Sum is Equal to a Given Value X in C++

Given a sorted doubly linked list containing integer values. The goal is to find triplets whose product is equal to the given value x. If input linked list is 3−4−1−2 and x is 6 then count will be 1 (triplet (3,1,2) )

For Example

Input

linked list: [ 3−4−13−5−10−10−0 ] x=20

Output

Count of triplets in a sorted doubly linked list whose product is equal to a given
value x are: 2

Explanation

Triplets will be:
( 3,4,13 ) and ( 10,10,0 )

Input

linked list: [ 4−3−1−5−2−4−2 ] x=8

Output

Count of triplets in a sorted doubly linked list whose product is equal to a given
value x are: 6

Explanation

Triplets will be:
( 4,3,1), (1,5,2), (3,1,4), (1,5,2), (4,2,2) and (2,4,2),

Approach used in the below program is as follows −

In this approach.

• We are taking a linked list node as struct containing int data part and self−referential next and previous pointers.

• Function insert_node(struct block** head, int data) adds the node at the head of linked list with data.

• Function Product_x(struct block* head, int x) takes the pointer to the head of doubly linked list and integer x and returns the count of triplets of nodes having product of data part as x.

• Take the initial count as 0.

• Take three pointers temp_1, temp_2 and temp_3 of type struct block.

• Starting from temp_1 pointing to the head of the linked list, temp_2 pointing to next to temp_1 and temp_3 pointing to the next to temp_3, we have three pointers pointing to the first three nodes.

• Traverse using these pointers until the last node.

• If current data parts of all above pointers have product as x. ((temp_1−>data + temp_2−>data + temp_3−>data) == x) then increment count.

• At the end we counted the number of triplets and stored in count.

• Return count as result.

Example

 Live Demo

#include <iostream>
using namespace std;
struct block{
   int data;
   struct block *next, *prev;
};
void insert_node(struct block** head, int data){
   struct block* ptr = new block();
   ptr−>data = data;
   ptr−>next = NULL;
   ptr−>prev = NULL;
   if ((*head) == NULL){
      (*head) = ptr;
   } else {
      ptr−>next = *head;
      (*head)−>prev = ptr;
      (*head) = ptr;
   }
}
int sum_x(struct block* head, int x){
   int count = 0;
   struct block *temp_1, *temp_2, *temp_3;
   for (temp_1 = head; temp_1!= NULL; temp_1 = temp_1−>next){
      for (temp_2 = temp_1−>next; temp_2 != NULL; temp_2 = temp_2−>next){
         for (temp_3 = temp_2−>next; temp_3!= NULL; temp_3 = temp_3−>next){
            if ((temp_1−>data + temp_2−>data + temp_3−>data) == x){
               count++;
            }
         }
      }
   }
   return count;
}
int main(){
   struct block* head = NULL;
   insert_node(&head, 200);
   insert_node(&head, 100);
   insert_node(&head, 16);
   insert_node(&head, 14);
   insert_node(&head, 10);
   insert_node(&head, 10);
   insert_node(&head, 2);
   int x = 22;
   cout<<"Count of triplets in a sorted doubly linked list whose sum is equal to a given value x
   are: "<<sum_x(head, x);
   return 0;
}

Output

If we run the above code it will generate the following output −

Count of triplets in a sorted doubly linked list whose sum is equal to a given value x are: 1