How to Check if a Deque is Empty in C++?

In C++, a deque is a container provided by the STL library that is similar to a queue. However, unlike queues, it allows insertion and deletion from both ends. In this article, we will learn how to determine whether a deque is empty or not in C++.

Example:

Input:
myDeque = {2, 4, 6 }

Output:
dq1 is not Empty.

Checking Whether a Deque is Empty in C++

To check if a std::deque is empty or not in C++, we can use the std::deque::empty() member function which returns a boolean value true if the deque is empty and false if the deque is not empty.

Syntax of std::deque::empty()

dq_name.empty()

C++ Program to Check if a Deque is Empty

The below program demonstrates how we can check if a deque is empty or not in C++.

C++

// C++ Program to demonstrates how we can check if a deque
// is empty or not
#include <deque>
#include <iostream>
using namespace std;

int main()
{
    // Initialize a deque with few elements
    deque<int> dq = { 1, 2, 3 };

    // Check if deque is empty
    if (dq.empty()) {
        cout << "Deque is empty" << endl;
    }
    else {
        cout << "Deque is not empty" << endl;
    }

    // Delete elements from the deque
    dq.pop_back();
    dq.pop_back();
    dq.pop_back();

    // Now check if a deque is empty or not
    cout << "After Removal: ";
    if (dq.empty()) {
        cout << "Deque is empty" << endl;
    }
    else {
        cout << "Deque is not empty" << endl;
    }

    return 0;
}

Output

Deque is not empty
After Removal: Deque is empty

Time Complexity: O(1)
Auxiliary Space: O(1)