double ended queue using linked List - Data Structure algorithm by developerIndian

Updated:13/01/2024 by Computer Hope

In this tutorial, you will learn what a double ended queue using linked List is. Also, you will find implementation of double ended queue using linked List in C, C++, Java and Python.

      #include<stdio.h>
#include<conio.h>
struct queue
 {  int no;
    struct queue *next;
 };
struct queue *front=NULL,*rear=NULL;
void insertrear(int val)
 {
 struct queue *q;
    q=(struct queue *)malloc(sizeof(struct queue));
    q->no=val;
    q->next=NULL;
    if(front==NULL)
      { front=rear=q;
	return;
      }
    rear->next=q;
    rear=q;
 }
void insertfront(int val)
  {
  struct queue *q;
  q=(struct queue *)malloc(sizeof(struct queue));
  q->no=val;
  q->next=front;
  if(front==NULL)
   {
    front=rear=q;
    return;
   }
  front=q;
 }
int deletefront()
  {int val;
   struct queue *q;
   if(front==NULL)
     { printf("\nQueue is Empty");
       return -999;
     }
   q=front;
   val=front->no;
   if(front==rear)
      front=rear=NULL;
   else
     front=front->next;
   free(q);
   return val;
  }
int deleterear()
 { int val;
   struct queue *q=front ;
   if(front==NULL)
    { printf("\nQueue is Empty");
      return -999;
     }
  val=rear->no;
  if(front==rear)
    front=rear=NULL;
  else
   { while(q->next->next!=NULL)
        q=q->next;
     rear=q;
     q=q->next;
     rear->next=NULL; }
  free(q);
  return val;
}
void show()
  {
   struct queue *q=front;
   if(front==NULL)
    { printf("\nQueue is Empty");
      return; }
  q=front;
  while(q!=NULL)
   { printf("%d\t",q->no);
     q=q->next;
   }
  }
void main()
 { int  ch,n;
   do
     {
      printf("\n1. Insert in Front");
      printf("\n2. Insert in Rear");
      printf("\n3. Delete from Front");
      printf("\n4. Delete from Rear");
      printf("\n5. Show");
      printf("\n0. Exit");
      printf("\n\nEnter Your Choice");
      scanf("%d",&ch);
       switch(ch)
         { case 1:printf("\nEnter Number ");
	            scanf("%d",&n);
	            insertfront(n);
	             break;
           case 2:printf("\nEnter Number ");
	            scanf("%d",&n);
	            insertrear(n);
	            break;
           case 3 :n=deletefront();
	             if(n!=-999)
	                printf("\n%d deleted",n);
	              break;
           case 4: n=deleterear();
	            if(n!=-999)
	               printf("\n%d deleted",n);
	            break;
           case 5 : show( );
	             break;
           case 0:break;
           default:printf("\nWrong Choice");
      }
   } while( ch != 0 ) ;
}