Stacks and Queues

Stack Push/Pop

Push values onto a stack and pop them back in last-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() {
    vector<int> stack;
    for (int value : {10, 20, 30}) stack.push_back(value);
    vector<int> popped;
    while (!stack.empty()) {
        popped.push_back(stack.back());
        stack.pop_back();
    }
    cout << render(popped) << endl;
}

Complexity

  • Time: O(1) per push/pop
  • 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.
top The top is the most recently pushed value.
LIFO A stack removes values in last-in, first-out order.