Implement Sorted Doubly Linked List in C++

In data structure Link List is a linear collection of data elements. Each element or node of a list is comprising of two items - the data and a reference to the next node. The last node has a reference to null. Into a linked list the entry point is called the head of the list.

A doubly linked list consists of a set of sequentially linked records called nodes. Each node contains three fields: one data field and two link fields; references to the previous and to the next node in the sequence of nodes field.

In case of sorted doubly linked list, according to the values of the sorted data field values the linked list will remain sorted.

Algorithm

Begin
   function createnode() to insert node in the list:
      it creates a newnode and inserts the number in the data field of the newnode.
      It checks whether the list is empty or not. If the list is empty put the node as first element and update head.
      Both prev and next pointers will be initialized with NULL.
      If list is not empty, then this newnode will be inserted into the existing linked list in such a way that ultimately the linked list will remain sorted.
      Prev and next pointers will be updated accordingly.
End
Begin
   function display_head() to display the list from the head:
      Initialize c=0.
      Initialize pointer variable with the head node address
      while (c <= i )
         Print the node info
         Update pointer variable
         Increment c.
End
Begin
   function dispslay_tail() to display the list from the tail:
      Initialize m=0.
      Initialize pointer variable with the tail node address
      while (m <= i )
         Print the node info
         Update pointer variable
         Increment m.
End

Example Code

#include<iostream>
using namespace std;
struct nod {
   int d;
   nod *n, *p;
}
*p = NULL, *head = NULL, *r = NULL, *np = NULL, *tail = NULL;
int c = 0;
void createnode(int n) {
   np = new nod;
   np->d = n;
   np->n = NULL;
   np->p = NULL;
   if (c == 0) {
      tail = np;
      head = np;
      p = head;
      p->n = head;
      p->p = head;
      c++;
   } else if (c == 1) {
      p = head;
      r = p;
      if (np->d < p->d) {
         np->n = p;
         p->p = np;
         head = np;
         p->n = np;
         np->p = p;
         tail = p;
      } else if (np->d > p->d) {
         p->n = np;
         np->p = p;
         np->n= head;
         p->p = np;
      }
      c++;
   } else {
      p = head;
      r = p;
      if (np->d < p->d) {
         np->n = p;
         p->p = np;
         head = np;
         do {
            p = p->n;
         }
         while (p->n != r);
            tail = p;
            p->n = np;
            np->p = p;
      } else if (np->d > p->d) {
         while (p->n != head && np->d > p->d) {
            r = p;
            p = p->n;
            if (p->n == head && (p->d < np->d)) {
               p->n = np;
               np->p = p;
               np->n = head;
               tail = np;
               head->p = np;
               break;
            } else if (np->d< p->d) {
               r->n= np;
               np->p = r;
               np->n= p;
               p->p= np;
               if (p->n != head) {
                  do {
                     p = p->n;
                  }
                  while (p->n != head);
               }
               tail = p;
               break;
            }
         }
      }
   }
}
void display_head(int i) {
   nod *t = head;
   int c = 0;
   while (c <= i) {
      cout<<t->d<<"\t";
      t = t->n;
      c++;
   }
   cout<<endl;
}
void display_tail(int i) {
   nod *t = tail;
   int m = 0;
   while (m <= i) {
      cout<<t->d<<"\t";
      t = t->p;
      m++;
   }
   cout<<endl;
}
int main() {
   int i = 0, n, a, ch;
   cout<<"enter the no of nodes\n";
   cin>>n;
   while (i < n) {
      cout<<"\nenter value of node\n";
      cin>>a;
      createnode(a);
      i++;
   }
   cout<<"\nsorting Doubly Linked List head first\n";
   display_head(n);
   cout<<"\nsorting Doubly Linked List tail first\n";
   display_tail(n);
}

Output

enter the no of nodes
5
enter value of node
7
enter value of node
4
enter value of node
6
enter value of node
2
enter value of node
1
sorting Doubly Linked List head first
1 2 4 6 7 1
sorting Doubly Linked List tail first
7 6 4 2 1 7