Queue Enqueue/Dequeue

Enqueue values at the back and dequeue them from the front in first-in, first-out order.

Algorithm

The replay uses the same three values in every language, so this C++ DSA implementation can be compared directly with the rest of the DSA track.

Basic Implementation

basic.cpp

#include <deque>
#include <iostream>
#include <sstream>
#include <string>
#include <vector>
using namespace std;

string render(const vector<int>& values) {
    ostringstream out;
    for (size_t i = 0; i < values.size(); ++i) {
        if (i > 0) out << " -> ";
        out << values[i];
    }
    return out.str();
}

int main() {
    deque<int> queue;
    for (int value : {10, 20, 30}) queue.push_back(value);
    vector<int> removed;
    while (!queue.empty()) {
        removed.push_back(queue.front());
        queue.pop_front();
    }
    cout << render(removed) << endl;
}

Complexity

Time: O(1) per operation with a real queue
Space: O(n)

Implementation notes

Keep the explicit stack/queue operations. Library shortcuts that only produce the final list hide the data-structure behavior this lesson is meant to replay.
The final output uses a deterministic a -> b -> c format for cross-language comparison.

front The front is the oldest value still waiting in the queue.

FIFO A queue removes values in first-in, first-out order.