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;
        size = 0;
    }
    
 void push(int x) {
        Node* new_Node = new Node();
        new_Node->data = x;
        new_Node->next = top;
        top = new_Node;
        size++;
    }

void push_stk(Node** topRef, int data) {
    // Allocate memory for new node
    Node* newNode = new Node();
    newNode->data = data;
    newNode->next = *topRef;

    // Set the new node as the top of the stack
    *topRef = newNode;
}    
 void pop() {
        if (top == NULL) {
            cout << "Stack is empty!" << endl;
            return;
        }
        Node* temp = top;
        top = top->next;
        size--;
        delete temp;
    }
    
void sortStack(Node** top) {
    if (*top == NULL || (*top)->next == NULL) {
        // There is only one element in the stack, so it is already sorted.
        return;
    }

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

    while (current != NULL) {
        next = current->next;
        current->next = prev;
        prev = current;
        current = next;
    }

     // Sort from the top of the stack by reversing the stack
    *top = prev;

    // Now we can use a temporary stack to sort the elements
    Node* tempStack = NULL;
    while (*top != NULL) {
        int temp = (*top)->data;
        (*top) = (*top)->next;

        while (tempStack != NULL && tempStack->data > temp) {
        // Pop elements from the temporary stack to the original stack 
		// until we find a position for the current element.
            push_stk(top, tempStack->data);
            tempStack = tempStack->next;
        }

        push_stk(&tempStack, temp);
    }
    // Set the original stack to the elements that were sorted.  
    *top = tempStack;  
}
    void display() {
        if (top == NULL) {
            cout << "Stack is empty!" << endl;
            return;
        }
        Node* temp = top;
        cout << "Stack elements are: ";
        while (temp != NULL) {
            cout << temp->data << " ";
            temp = temp->next;
        }
        cout << endl;
    }
};

int main() {
    Stack stk;
    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();
	cout << "\nSorted elements of the said stack:\n";
	stk.sortStack(&stk.top);
	stk.display(); 
	cout << "\nInput two more elements:\n";
	stk.push(35);
    stk.push(29);
    stk.display();     
    cout << "\nSorted elements of the said stack:\n";
	stk.sortStack(&stk.top);
	stk.display(); 
    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.