C++ Program to Implement Deque in STL

Double Ended Queue is a Queue data structure in which the insertion and deletion operations are performed at both the ends (front and rear). Data can be inserted at both front and rear positions and can be deleted from both front and rear positions.

Algorithm

Begin
   Declare deque vector and iterator.
   Take the input as per choice.
   Call the functions within switch operation:
   d.size() = Returns the size of queue.
   d.push_back() = It is used to push elements into a deque from the back.
   d.push_front() = It is used to push elements into a deque from the front.
   d.pop_back() = It is used to pop or remove elements from a deque from the back.
   d.pop_front() = It is used to pop or remove elements from a deque from the front.
   d.front() = Returns the front elements of deque.
   d.back() = Returns the back elements of deque.
   Print the elements of deque.
End.

Example Code

#include<iostream>
#include <deque>
#include <string>
#include <cstdlib>
using namespace std;
int main() {
   deque<int> d;
   deque<int>::iterator it;
   int c, item;
   while (1) {
      cout<<"1.Size of the Deque"<<endl;
      cout<<"2.Insert Element at the End"<<endl;
      cout<<"3.Insert Element at the Front"<<endl;
      cout<<"4.Delete Element at the End"<<endl;
      cout<<"5.Delete Element at the Front"<<endl;
      cout<<"6.Front Element at Deque"<<endl;
      cout<<"7.Last Element at Deque"<<endl;
      cout<<"8.Display Deque"<<endl;
      cout<<"9.Exit"<<endl;
      cout<<"Enter your Choice: ";
      cin>>c;
      switch(c) {
         case 1:
            cout<<"Size of the Deque: "<<d.size()<<endl;
         break;
         case 2:
            cout<<"Enter value to be inserted at the end: ";
            cin>>item;
            d.push_back(item);
         break;
         case 3:
            cout<<"Enter value to be inserted at the front: ";
            cin>>item;
            d.push_front(item);
         break;
         case 4:
            item = d.back();
            d.pop_back();
            cout<<"Element "<<item<<" deleted"<<endl;
         break;
         case 5:
            item = d.front();
            d.pop_front();
            cout<<"Element "<<item<<" deleted"<<endl;
         break;
         case 6:
            cout<<"Front Element of the Deque: ";
            cout<<d.front()<<endl;
         break;
         case 7:
            cout<<"Back Element of the Deque: ";
            cout<<d.back()<<endl;
         break;
         case 8:
            cout<<"Elements of Deque: ";
            for (it = d.begin(); it != d.end(); it++)
               cout<<*it<<" ";
            cout<<endl;
         break;
         case 9:
            exit(1);
         break;
         default:
            cout<<"Wrong Choice"<<endl;
      }
   }
   return 0;
}

Output

1.Size of the Deque
2.Insert Element at the End
3.Insert Element at the Front
4.Delete Element at the End
5.Delete Element at the Front
6.Front Element at Deque
7.Last Element at Deque
8.Display Deque
9.Exit

Enter your Choice: 1
Size of the Deque: 0
1.Size of the Deque
2.Insert Element at the End
3.Insert Element at the Front
4.Delete Element at the End
5.Delete Element at the Front
6.Front Element at Deque
7.Last Element at Deque
8.Display Deque
9.Exit

Enter your Choice: 2
Enter value to be inserted at the end: 1
1.Size of the Deque
2.Insert Element at the End
3.Insert Element at the Front
4.Delete Element at the End
5.Delete Element at the Front
6.Front Element at Deque
7.Last Element at Deque
8.Display Deque
9.Exit

Enter your Choice: 3
Enter value to be inserted at the front: 2
1.Size of the Deque
2.Insert Element at the End
3.Insert Element at the Front
4.Delete Element at the End
5.Delete Element at the Front
6.Front Element at Deque
7.Last Element at Deque
8.Display Deque
9.Exit

Enter your Choice: 6
Front Element of the Deque: 2
1.Size of the Deque
2.Insert Element at the End
3.Insert Element at the Front
4.Delete Element at the End
5.Delete Element at the Front
6.Front Element at Deque
7.Last Element at Deque
8.Display Deque
9.Exit

Enter your Choice: 7
Back Element of the Deque: 1
1.Size of the Deque
2.Insert Element at the End
3.Insert Element at the Front
4.Delete Element at the End
5.Delete Element at the Front
6.Front Element at Deque
7.Last Element at Deque
8.Display Deque
9.Exit

Enter your Choice: 1
Size of the Deque: 2
1.Size of the Deque
2.Insert Element at the End
3.Insert Element at the Front
4.Delete Element at the End
5.Delete Element at the Front
6.Front Element at Deque
7.Last Element at Deque
8.Display Deque
9.Exit

Enter your Choice: 8
Elements of Deque: 2 1
1.Size of the Deque
2.Insert Element at the End
3.Insert Element at the Front
4.Delete Element at the End
5.Delete Element at the Front
6.Front Element at Deque
7.Last Element at Deque
8.Display Deque
9.Exit

Enter your Choice: 2
Enter value to be inserted at the end: 4
1.Size of the Deque
2.Insert Element at the End
3.Insert Element at the Front
4.Delete Element at the End
5.Delete Element at the Front
6.Front Element at Deque
7.Last Element at Deque
8.Display Deque
9.Exit

Enter your Choice: 3
Enter value to be inserted at the front: 5
1.Size of the Deque
2.Insert Element at the End
3.Insert Element at the Front
4.Delete Element at the End
5.Delete Element at the Front
6.Front Element at Deque
7.Last Element at Deque
8.Display Deque
9.Exit

Enter your Choice: 8
Elements of Deque: 5 2 1 4
1.Size of the Deque
2.Insert Element at the End
3.Insert Element at the Front
4.Delete Element at the End
5.Delete Element at the Front
6.Front Element at Deque
7.Last Element at Deque
8.Display Deque
9.Exit

Enter your Choice: 4
Element 4 deleted
1.Size of the Deque
2.Insert Element at the End
3.Insert Element at the Front
4.Delete Element at the End
5.Delete Element at the Front
6.Front Element at Deque
7.Last Element at Deque
8.Display Deque
9.Exit

Enter your Choice: 5
Element 5 deleted
1.Size of the Deque
2.Insert Element at the End
3.Insert Element at the Front
4.Delete Element at the End
5.Delete Element at the Front
6.Front Element at Deque
7.Last Element at Deque
8.Display Deque
9.Exit

Enter your Choice: 8
Elements of Deque: 2 1
1.Size of the Deque
2.Insert Element at the End
3.Insert Element at the Front
4.Delete Element at the End
5.Delete Element at the Front
6.Front Element at Deque
7.Last Element at Deque
8.Display Deque
9.Exit
Enter your Choice: 9