C++ Stack Exercises: K^th element of a stack from top position

Last update on April 14 2025 12:44:32 (UTC/GMT +8 hours)

14. Get the Kth Element from the Top of an Array-Based Stack

Write a C++ program to get the K^th element of a stack from top position.

Test Data:
Input some elements onto the stack:
Stack elements are: 4 3 2 1
Remove 2 from the said stack:
2nd element from the top of the stack: 3

Sample Solution:

C++ Code:

#include <iostream>

using namespace std;
#define MAX_SIZE 15 // Maximum size of stack

class Stack {
private:
    int top; // Index of top element
    int arr[MAX_SIZE]; // Array to store elements
public:
    Stack() {
        top = -1; // Initialize top index to -1 (empty stack)
    }

    bool push(int x) {
        if (isFull()) {
            cout << "Stack is full!" << endl; // Display message if stack is full
            return false; // Return false to indicate failure in pushing element
        }
        // Increment top index and add element to array
        arr[++top] = x; 
        return true; // Return true to indicate successful element addition
    }

    int pop() {
        if (isEmpty()) {
            cout << "Stack underflow" << endl; // Display message if stack is empty
            return 0; // Return 0 to indicate failure in popping element
        }
        // Return top element and decrement top index
        return arr[top--]; 
    }

    int peek() {
        if (isEmpty()) {
            cout << "Stack is empty" << endl; // Display message if stack is empty
            return 0; // Return 0 to indicate failure in peeking element
        }
        // Return top element without modifying top index
        return arr[top]; 
    }

    bool isEmpty() {
        // Stack is empty if top index is -1
        return (top < 0); 
    }

    bool isFull() {
        // Stack is full if top index is equal to MAX_SIZE - 1
        return (top >= MAX_SIZE - 1); 
    }

    void display() {
        if (top < 0) {
            cout << "Stack is empty" << endl; // Display message if stack is empty
            return;
        }
        cout << "\nStack elements are: ";
        for (int i = top; i >= 0; i--)
            cout << arr[i] << " "; // Display elements of the stack
        cout << endl;
    }  

    int getSize() {
        return top + 1; // Return the size of the stack
    }       

    int get_Kth_element_from_top(Stack& stk, int k) {
        if (stk.isEmpty()) {
            cout << "Stack is empty." << endl; // Display message if the stack is empty
            return -1;
        }
        if (k < 1 || k > stk.getSize()) {
            cout << "Invalid k value." << endl; // Display message for invalid k value
            return -1;
        }
        int size = stk.getSize();
        int temp[size];
        int count = 0;

        // Copy stack elements into a temporary array
        while (!stk.isEmpty()) {
            temp[count++] = stk.pop();
        }

        // Get kth element from top of stack
        int kthElement = temp[k - 1]; 

        // Place elements back in their original order on the stack
        for (int i = count - 1; i >= 0; i--) {
            stk.push(temp[i]);
        }
        return kthElement; // Return the kth element from the top of the stack
    }
};

int main() {
    Stack stk; 
    cout << "Input some elements onto the stack:";
    stk.push(1);
    stk.push(2);
    stk.push(3);
    stk.push(4);
    stk.display();
    cout << "\nRemove 2 from the said stack:";
    int z = stk.get_Kth_element_from_top(stk, 2); // Get the 2nd element from the top of the stack
    cout << "\n2nd element from the top of the stack: " << z;
    cout << "\n\nInput two more elements onto the stack:";
    stk.push(-1);
    stk.push(0);
    stk.display();
    z = stk.get_Kth_element_from_top(stk, 1); // Get the 1st element from the top of the stack
    cout << "\n1st element from the top of the stack: " << z;
    z = stk.get_Kth_element_from_top(stk, 3); // Get the 3rd element from the top of the stack
    cout << "\n3rd element from the top of the stack: " << z;
    z = stk.get_Kth_element_from_top(stk, 6); // Get the 6th element from the top of the stack
    cout << "\n6th element from the top of the stack: " << z;
    cout << endl;
}

Sample Output:

Input some elements onto the stack:
Stack elements are: 4 3 2 1

Remove 2 from the said stack:
2nd element from the top of the stack: 3

Input two more elements onto the stack:
Stack elements are: 0 -1 4 3 2 1

1st element from the top of the stack: 0
3rd element from the top of the stack: 4
6th element from the top of the stack: 1

Flowchart:

For more Practice: Solve these Related Problems:

• Write a C++ program to retrieve the kth element from the top in an array-based stack with bounds checking.
• Develop a C++ program that calculates the kth position in an array-based stack and prints the corresponding element.
• Design a C++ program to fetch the kth element from an array-based stack and handle invalid k values gracefully.
• Implement a C++ program to access the kth item in a stack (using an array) and output its value without altering the stack.

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