Applications of Stack and Queue Algorithms in C++

In computer science, stacks and queues are two fundamental data structures. They have wide applications in programming and algorithms. This article will detail the concepts, implementations, and common applications of these two data structures, along with code examples to help beginners understand.

Stack

Overview of Stack

A stack is a Last In First Out (LIFO) data structure. This means that the last element added to the stack is the first one to be removed. You can think of it as a stack of plates where only the top plate can be taken off.

Basic Operations of Stack

1. Push: Adds an element to the top of the stack.
2. Pop: Removes and returns the top element of the stack.
3. Top: Returns the top element without removing it.
4. IsEmpty: Checks if the stack contains any elements.

C++ Implementation

The C++ STL provides the <span>stack</span> container class, which makes it easy to create and use stacks. Here is an example code using <span>stack</span>:

#include <iostream>
#include <stack>
int main() {
    std::stack<int> myStack;
    // Push elements
    myStack.push(1);
    myStack.push(2);
    myStack.push(3);
    // View and print top element
    std::cout << "Top element: " << myStack.top() << std::endl;
    // Pop an element
    myStack.pop();
    // View top element again
    std::cout << "After popping, top element: " << myStack.top() << std::endl;
    // Check if empty
    if (!myStack.empty()) {
        std::cout << "Stack is not empty" << std::endl;
        while (!myStack.empty()) {
            std::cout << "Popped number: " << myStack.top() << std::endl;
            myStack.pop();
        }
        std::cout << "Now the stack is empty" << std::endl;
    } else {
        std::cout << "Stack is empty!" << std::endl;
    }
    return 0;
}

Explanation of the Example

• This program first creates a stack of integers and then pushes three integers (1, 2, 3) onto it.
• It uses the <span>top()</span> method to view the current top value, then calls the <span>pop()</span> method to remove that value and retrieves the new top value again.
• Finally, it pops all remaining values in a loop and displays each popped number.

Queue

Overview of Queue

A queue is a First In First Out (FIFO) data structure. This means that the first member added to the queue will be the first one to be processed. It is like a line of people waiting to buy tickets, where people enter in order and leave in the same order.

Basic Operations of Queue

1. Enqueue: Adds a new item to the end of the queue.
2. Dequeue: Removes and returns the front item of the queue.
3. Front: Returns the front item without removing it.
4. IsEmpty: Checks if the queue contains any items.

C++ Implementation

The C++ STL provides the <span>queue</span> container class, which makes it easy to create and use queues. Here is an example code using <span>queue</span>:

#include <iostream>
#include <queue>
int main() {
    std::queue<int> myQueue;
    // Enqueue elements
    for(int i = 0; i < 5; i++) {
        myQueue.push(i * 10);
    }
    std::cout << "Front element: " << myQueue.front() << std::endl;
    myQueue.pop();
    std::cout << "After popping, front element: " << myQueue.front() << std::endl;
    if (!myQueue.empty()) {
        while (!myQueue.empty()) {
            std::cout << "Dequeued element: " << myQueue.front() << std::endl;
            myQueue.pop();
        }
    } else {
        std::cerr << "Queue is empty!" << std::endl;
    }
    return 0;
}

This program creates a queue of integers using the standard library. It ensures that we first leave the first element in the queue and then adds new elements.

Running the code will show how FIFO data flows. When users continuously dequeue, they will see each element being processed in the order they were added.

Conclusion

This article demonstrates the stack and queue data structures in C++ through simple examples and their basic operations. These concepts are not only applicable to specific programming languages but are also crucial for classic computer science problems such as parentheses matching and graph searching. The thinking behind these structures is also applied in more complex data structures. Therefore, it is essential to master these basics to prepare for deeper learning and practice.