Deque - Introduction and Applications

Last Updated : 11 May, 2025

Deque or Double Ended Queue is a generalized version of Queue data structure that allows insert and delete at both ends. Below is an example program of deque in different languages.

Deque can act as both Stack and Queue
It is useful in many problems where we need to have a subset of all operations also like insert/remove at front and insert/remove at the end.
It is typically implemented either using a doubly linked list or circular array.

Implementations of Deque in Different Languages

Below are example programs in different languages.

C++

#include <iostream>
#include <deque>

using namespace std;

int main() {
    deque<int> dq;

    dq.push_back(10);
    dq.push_back(20);
    dq.push_front(30);

    // Print deque elements
    for (int x : dq) cout << x << " ";
    cout << endl;

    // Pop from front and back
    dq.pop_front();
    dq.pop_back();

    // Print deque elements after pop
    for (int x : dq) cout << x << " ";
    
    return 0;
}

Java

import java.util.ArrayDeque;
import java.util.Deque;

public class Main {
    public static void main(String[] args) {
        Deque<Integer> dq = new ArrayDeque<>();

        dq.addLast(10);
        dq.addLast(20);
        dq.addFirst(30);

        // Print deque elements
        for (int x : dq) System.out.print(x + " ");
        System.out.println();

        // Pop from front and back
        dq.removeFirst();
        dq.removeLast();

        // Print deque elements after pop
        for (int x : dq) System.out.print(x + " ");
    }
}

Python

from collections import deque

dq = deque()

dq.append(10)
dq.append(20)
dq.appendleft(30)

# Print deque elements
print(' '.join(map(str, dq)))

# Pop from front and back
dq.popleft()
dq.pop()

# Print deque elements after pop
print(' '.join(map(str, dq)))

using System;
using System.Collections.Generic;

class Program {
    static void Main() {
        Deque<int> dq = new Deque<int>();

        dq.AddLast(10);
        dq.AddLast(20);
        dq.AddFirst(30);

        // Print deque elements
        foreach (int x in dq) Console.Write(x + " ");
        Console.WriteLine();

        // Pop from front and back
        dq.RemoveFirst();
        dq.RemoveLast();

        // Print deque elements after pop
        foreach (int x in dq) Console.Write(x + " ");
    }
}

public class Deque<T> {
    private LinkedList<T> list = new LinkedList<T>();

    public void AddFirst(T value) { list.AddFirst(value); }
    public void AddLast(T value) { list.AddLast(value); }
    public void RemoveFirst() { list.RemoveFirst(); }
    public void RemoveLast() { list.RemoveLast(); }
    public IEnumerator<T> GetEnumerator() { return list.GetEnumerator(); }
}

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