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How to Copy a One Deque to Another in C++?

Last Updated : 23 Jul, 2025

In C++, STL provides a container called deque (short for double-ended queue) that allows fast insertion and deletion at both its beginning and its end. In some scenarios, we may need to copy the contents of one deque to another. In this article, we will learn how to copy one deque to another in C++.

Example:

Input: 
deque1 = {10, 20, 30, 40, 50, 60}
Output: 

deque2: {10, 20, 30, 40, 50, 60}

For copying all the elements stored in one std::deque to another in C++, we can use the std::copy() function provided in the STL <algorithm> library that copies a range of elements from one container to another.

copy(oldDeque.begin(), oldDeque.end(), newDeque.begin());

Here,

• oldDeque.begin() is the iterator to the beginning of the original deque (oldDeque).
• oldDeque.end() is the iterator to the end of the original deque (oldDeque).
• newDeque.begin() is the iterator to the beginning of the destination deque(newDeque) where we have to copy the elements of the original deque.

The below program demonstrates how we can copy one deque to another using copy() function in C++.

// C++ Program to Copy One Deque to Another

#include <algorithm>
#include <deque>
#include <iostream>
using namespace std;

int main()
{
    // Original deque
    deque<int> oldDeque = { 1, 2, 3, 4, 5 };

    // destination deque
    deque<int> newDeque(oldDeque.size());

    // Copying Deque Using copy algorithm
    copy(oldDeque.begin(), oldDeque.end(),
         newDeque.begin());

    // Printing original deque
    cout << "Original deque:";
    for (const auto& elem : oldDeque) {
        cout << " " << elem;
    }
    cout << endl;

    // Printing copied deque
    cout << "Copied deque:";
    for (const auto& elem : newDeque) {
        cout << " " << elem;
    }
    cout << endl;

    return 0;
}

Original deque: 1 2 3 4 5
Copied deque: 1 2 3 4 5

Time Complexity: O(N), where n is the number of elements in each deque.
Auxiliary Space: O(N)

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