Queues and Stacks

Queue (FIFO)

• Definition: A queue is a linear data structure that follows the First In, First Out (FIFO) principle.
• Analogy: Think of people lining up at a ticket counter. The first person to join the line is the first to be served.

#include <iostream>

#include <queue>

using namespace std;

int main() {

    queue<int> q;

    // Enqueue elements into the queue

    q.push(10);

    q.push(20);

    q.push(30);

    cout << "Queue (FIFO):" << endl;

    while (!q.empty()) {

        cout << q.front() << " ";  // Access the front element

        q.pop();                   // Remove the front element

    }

    return 0;

}

while (!q.empty())

q → This is your queue object (e.g., queue q;).

q.empty() → This function returns true if the queue has no elements, otherwise false.

!q.empty() → The ! (logical NOT) operator flips the result:

If the queue is not empty, !q.empty() is true.

If the queue is empty, !q.empty() is false.

while (!q.empty()) → This loop continues to run as long as the queue has elements inside.

Stack (LIFO)

• Definition: A stack is a linear data structure that follows the Last In, First Out (LIFO) principle.
• Analogy: Imagine a stack of plates. The last plate placed on top is the first one you take off.

#include <iostream>

#include <stack>

using namespace std;

int main() {

    stack<int> s;

    // Push elements onto the stack

    s.push(10);

    s.push(20);

    s.push(30);

    cout << "Stack (LIFO):" << endl;

    while (!s.empty()) {

        cout << s.top() << " ";  // Access the top element

        s.pop();                 // Remove the top element

    }

    return 0;

}

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