C++ Stack Exercises: Find the middle element(s) of a stack (using a vector)

Last update on April 14 2025 12:47:58 (UTC/GMT +8 hours)

27. Find the Middle Element(s) of a Vector-Based Stack

Write a C++ program to find the middle element(s) of a stack (using a vector).

Test Data:
Create a stack object:
Input and store (using vector) some elements onto the stack:
Stack elements are: 1 3 2 6 5 -1
Middle element(s) of the said stack elements:
2 6

Sample Solution:

C++ Code:

#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

class Stack {
private:
    vector<int> elements; // Vector to store elements

public:
    void push(int element) {
        elements.push_back(element); // Add element to the end of the vector
    }

    void pop() {
        if (elements.empty()) {
            cout << "Stack is full" << endl; // Display full message if the stack is empty
        } else {
            elements.pop_back(); // Remove the last element from the vector
        }
    }

    int top() {
        if (elements.empty()) {
            cout << "Stack is empty" << endl; // Display empty message if the stack is empty
            return 0;
        } else {
            return elements.back(); // Return the last element in the vector
        }
    }

    bool empty() {
        return elements.empty(); // Check if the vector is empty
    }

    void display() {
        vector<int> v = elements;
        if (v.empty()) {
            cout << "Stack is empty" << endl; // Display empty message if the stack is empty
            return;
        }
        cout << "Stack elements are: ";
        for (int i = 0; i < v.size(); i++) {
            cout << v[i] << " "; // Display the elements of the stack
        }
        cout << endl;
    }

    // Function to get the middle element(s) of the stack
    vector<int> getMiddleElements() {
        vector<int> result;
        int size = elements.size();
        if (size % 2 == 0) {
            result.push_back(elements[size / 2 - 1]); // Add middle element if stack size is even
        }
        result.push_back(elements[size / 2]); // Add middle element if stack size is odd
        return result;
    }
};

int main() {
    Stack stack;
    cout << "Create a stack object:\n"; // Initialize a stack
    cout << "\nInput and store (using vector) some elements onto the stack:\n";
    stack.push(1);
    stack.push(3);
    stack.push(2);
    stack.push(6);
    stack.push(5);
    stack.push(-1);
    stack.display();
    cout << "\nMiddle element(s) of the said stack elements:\n";
    vector<int> middleElements = stack.getMiddleElements();
    for (int i = 0; i < middleElements.size(); i++) {
        cout << middleElements[i] << " "; // Display middle element(s)
    }
    cout << "\n\nInput one more element:\n";
    stack.push(0);
    stack.display();
    cout << "\nMiddle element(s) of the said stack elements:\n";
    middleElements = stack.getMiddleElements();
    for (int i = 0; i < middleElements.size(); i++) {
        cout << middleElements[i] << " "; // Display middle element(s)
    }
    cout << endl;
    return 0;
}

Sample Output:

Create a stack object:

Input and store (using vector) some elements onto the stack:
Stack elements are: 1 3 2 6 5 -1 

Middle element(s) of the said stack elements:
2 6 

Input one more element:
Stack elements are: 1 3 2 6 5 -1 0 

Middle element(s) of the said stack elements:
6 

Flowchart:

For more Practice: Solve these Related Problems:

• Write a C++ program to determine the middle element(s) in a vector-based stack and print them without modifying the vector.
• Develop a C++ program that computes the middle index of a vector-based stack and displays the corresponding value(s).
• Design a C++ program to implement a vector-based stack and retrieve the central element(s) for both even and odd cases.
• Implement a C++ program to access and print the middle element(s) in a vector-based stack with careful boundary checks.

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