C++ Program to Implement Dequeue

Dequeue or Double Ended Queue is a generalized version of Queue data structure that allows insert and delete at both ends.

Some basic operations of dequeue are −

insert_at_beg(): inserts an item at the front of Dequeue.

insert_at_end(): inserts an item at the rear of Dequeue.

delete_fr_beg(): Deletes an item from front of Dequeue.

delete_fr_rear(): Deletes an item from rear of Dequeue.

Following is a C++ program to implement Dequeue

Algorithm

Begin
   Declare a class dequeue to declare front f and rear r and following functions:
   function insert_at_beg(int) to insert item at front:
      If queue is not completely filled up, insert element at the front and update front and rear
      Otherwise print overflow.
   function insert_at_end(int) to insert item at rear:
      If queue is not completely filled up, insert element at the rear and update front and rear
      Otherwise print overflow.
   function delete_fr_beg() to delete item from front:
      If queue is empty, print underflow otherwise delete the front element and update front.
   function delete_fr_end() to delete item from end:
      If queue is empty, print underflow otherwise delete the rear element and update rear.
End

Example Code

#include<iostream>
using namespace std;
#define SIZE 10
class dequeue {
   int a[20],f,r;
   public:
      dequeue();
      void insert_at_beg(int);
      void insert_at_end(int);
      void delete_fr_front();
      void delete_fr_rear();
      void show();
};
dequeue::dequeue() {
   f=-1;
   r=-1;
}
void dequeue::insert_at_end(int i) {
   if(r>=SIZE-1) {
      cout<<"\n insertion is not possible, overflow!!!!";
   } else {
      if(f==-1) {
         f++;
         r++;
      } else {
         r=r+1;
      }
      a[r]=i;
      cout<<"\nInserted item is"<<a[r];
   }
}
void dequeue::insert_at_beg(int i) {
   if(f==-1) {
      f=0;
      a[++r]=i;
      cout<<"\n inserted element is:"<<i;
   } else if(f!=0) {
      a[--f]=i;
      cout<<"\n inserted element is:"<<i;
   } else {
      cout<<"\n insertion is not possible, overflow!!!";
   }
}
void dequeue::delete_fr_front() {
   if(f==-1) {
      cout<<"deletion is not possible::dequeue is empty";
      return;
   }
   else {
      cout<<"the deleted element is:"<<a[f];
      if(f==r) {
         f=r=-1;
         return;
      } else
         f=f+1;
      }
   }
   void dequeue::delete_fr_rear() {
      if(f==-1) {
         cout<<"deletion is not possible::dequeue is empty";
         return;
      }
      else {
         cout<<"the deleted element is:"<<a[r];
         if(f==r) {
            f=r=-1;
         } else
            r=r-1;
      }
   }
   void dequeue::show() {
      if(f==-1) {
         cout<<"Dequeue is empty";
      } else {
         for(int i=f;i<=r;i++) {
            cout<<a[i]<<" ";
         }
      }
   }
   int main() {
      int c,i;
      dequeue d;
      Do//perform switch opeartion {
      cout<<"\n 1.insert at beginning";
      cout<<"\n 2.insert at end";
      cout<<"\n 3.show";
      cout<<"\n 4.deletion from front";
      cout<<"\n 5.deletion from rear";
      cout<<"\n 6.exit";
      cout<<"\n enter your choice:";
      cin>>c;
      switch(c) {
         case 1:
            cout<<"enter the element to be inserted";
            cin>>i;
            d.insert_at_beg(i);
         break;
         case 2:
            cout<<"enter the element to be inserted";
            cin>>i;
            d.insert_at_end(i);
         break;
         case 3:
            d.show();
         break;
         case 4:
            d.delete_fr_front();
         break;
         case 5:
            d.delete_fr_rear();
         break;
         case 6:
            exit(1);
         break;
         default:
            cout<<"invalid choice";
         break;
      }
   } while(c!=7);
}

Output

1.insert at beginning
2.insert at end
3.show
4.deletion from front
5.deletion from rear
6.exit
enter your choice:4
deletion is not possible::dequeue is empty
1.insert at beginning
2.insert at end
3.show
4.deletion from front
5.deletion from rear
6.exit
enter your choice:5
deletion is not possible::dequeue is empty
1.insert at beginning
2.insert at end
3.show
4.deletion from front
5.deletion from rear
6.exit
enter your choice:1
enter the element to be inserted7

inserted element is:7
1.insert at beginning
2.insert at end
3.show
4.deletion from front
5.deletion from rear
6.exit
enter your choice:1
enter the element to be inserted6

insertion is not possible, overflow!!!
1.insert at beginning
2.insert at end
3.show
4.deletion from front
5.deletion from rear
6.exit
enter your choice:1
enter the element to be inserted4

insertion is not possible, overflow!!!
1.insert at beginning
2.insert at end
3.show
4.deletion from front
5.deletion from rear
6.exit
enter your choice:2
enter the element to be inserted6

Inserted item is6
1.insert at beginning
2.insert at end
3.show
4.deletion from front
5.deletion from rear
6.exit
enter your choice:2
enter the element to be inserted4

Inserted item is4
1.insert at beginning
2.insert at end
3.show
4.deletion from front
5.deletion from rear
6.exit
enter your choice:3
7 6 4
1.insert at beginning
2.insert at end
3.show
4.deletion from front
5.deletion from rear
6.exit
enter your choice:4
the deleted element is:7
1.insert at beginning
2.insert at end
3.show
4.deletion from front
5.deletion from rear
6.exit
enter your choice:5
the deleted element is:4
1.insert at beginning
2.insert at end
3.show
4.deletion from front
5.deletion from rear
6.exit
enter your choice:1
enter the element to be inserted7

inserted element is:7
1.insert at beginning
2.insert at end
3.show
4.deletion from front
5.deletion from rear
6.exit
enter your choice:3
7 6
1.insert at beginning
2.insert at end
3.show
4.deletion from front
5.deletion from rear
6.exit
enter your choice:6