C++ Stack Exercises: Sort the elements of a stack (using a linked list)

C++ Stack: Exercise-19 with Solution

Write a C++ program to sort the elements of a stack (using a linked list).

Test Data:
Input some elements onto the stack:
Stack elements are: 0 1 3 5 6
Sorted elements of the said stack:
Stack elements are: 6 5 3 1 0

Sample Solution:

C++ Code:

#include <iostream>

using namespace std;

// Define the node structure for the linked list
struct Node {
    int data;
    Node* next;
};

class Stack {
private:
    // This variable keeps track of the stack size
    int size;  

public:
    // Top-of-stack pointer
    Node* top;

    // Constructor to initialize an empty stack
    Stack() {
        top = NULL; // Initialize top pointer to NULL for an empty stack
        size = 0; // Initialize the size of the stack to zero
    }

    // Function to push an element onto the stack
    void push(int x) {
        Node* new_Node = new Node();
        new_Node->data = x;
        new_Node->next = top;
        top = new_Node;
        size++;
    }

    // Function to push elements onto the stack (helper function)
    void push_stk(Node** topRef, int data) {
        Node* newNode = new Node(); // Create a new node
        newNode->data = data; // Assign data to the new node
        newNode->next = *topRef; // Set the next of the new node to the current top node
        *topRef = newNode; // Update the top reference to the new node
    }    

    // Function to pop an element from the stack
    void pop() {
        if (top == NULL) {
            cout << "Stack is empty!" << endl; // Display message if the stack is empty
            return;
        }
        Node* temp = top; // Store the current top node
        top = top->next; // Move top to the next node
        size--; // Decrement the size of the stack
        delete temp; // Delete the previous top node
    }

    // Function to sort the elements of the stack in ascending order
    void sortStack(Node** top) {
        if (*top == NULL || (*top)->next == NULL) {
            // There is only one element in the stack, or the stack is empty, so it is already sorted.
            return;
        }

        Node* prev = NULL;
        Node* current = *top;
        Node* next = NULL;

        // Reverse the stack
        while (current != NULL) {
            next = current->next;
            current->next = prev;
            prev = current;
            current = next;
        }

        *top = prev; // Update the top pointer with the reversed stack

        // Temporary stack to sort elements
        Node* tempStack = NULL;
        while (*top != NULL) {
            int temp = (*top)->data;
            (*top) = (*top)->next;

            // Move elements to the temporary stack to sort
            while (tempStack != NULL && tempStack->data > temp) {
                push_stk(top, tempStack->data);
                tempStack = tempStack->next;
            }

            push_stk(&tempStack, temp); // Push the current element into the temporary stack
        }
        // Set the original stack to the elements that were sorted.  
        *top = tempStack;  
    }

    // Function to display the elements of the stack
    void display() {
        if (top == NULL) {
            cout << "Stack is empty!" << endl; // Display message if the stack is empty
            return;
        }
        Node* temp = top; // Create a temporary node to traverse the stack
        cout << "Stack elements are: ";
        while (temp != NULL) {
            cout << temp->data << " "; // Display the data of each node
            temp = temp->next; // Move to the next node
        }
        cout << endl;
    }
};

int main() {
    Stack stk; // Create an object of Stack class
    cout << "Input some elements onto the stack:\n";
    stk.push(6);
    stk.push(5);
    stk.push(3);
    stk.push(1);
    stk.push(0);
    stk.display(); // Display the elements in the stack
    cout << "\nSorted elements of the said stack:\n";
    stk.sortStack(&stk.top); // Sort the stack elements in ascending order
    stk.display(); // Display the sorted stack elements
    cout << "\nInput two more elements:\n";
    stk.push(35);
    stk.push(29);
    stk.display(); // Display the updated elements in the stack
    cout << "\nSorted elements of the said stack:\n";
    stk.sortStack(&stk.top); // Sort the stack elements in ascending order again
    stk.display(); // Display the sorted stack elements
    return 0;
}

Sample Output:

Input some elements onto the stack:
Stack elements are: 0 1 3 5 6 

Sorted elements of the said stack:
Stack elements are: 6 5 3 1 0 

Input two more elements:
Stack elements are: 29 35 6 5 3 1 0 

Sorted elements of the said stack:
Stack elements are: 35 29 6 5 3 1 0 

Flowchart:

CPP Code Editor:

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Previous C++ Exercise: Reverse the elements of a stack (using a linked list).
Next C++ Exercise: Implement a stack using a dynamic array with push, pop.