C++ - C++ Deque Part 1: Introduction to C++ Deque

A deque (double-ended queue) is a dynamic container in C++ that allows efficient insertions and deletions from both the front and the back. Unlike vectors, which provide efficient insertions and deletions only at the back, deques provide O(1) time complexity for both ends. They are implemented as a sequence of memory blocks rather than a contiguous array like vectors, which helps in faster insertions and deletions.

Example 1: Basic Deque Initialization and Printing

#include <iostream>

#include <deque>

int main() {

    std::deque<int> dq = {10, 20, 30, 40};

    for (int num : dq) {

        std::cout << num << " ";

    }

    return 0;

}

Explanation:

A deque dq is initialized with values {10, 20, 30, 40}.

A range-based for loop is used to iterate and print the elements.

Unlike vectors, deques allow easy insertion and deletion from both ends.

Output:

10 20 30 40

Example 2: Creating an Empty Deque and Checking if it’s Empty

#include <iostream>

#include <deque>

int main() {

    std::deque<int> dq;

    if (dq.empty()) {

        std::cout << "Deque is empty!" << std::endl;

    }

    return 0;

}

Explanation:

The .empty() function checks if the deque is empty.

Since dq is not initialized with elements, it prints "Deque is empty!".

Output:

Deque is empty!