C++ Stack Exercises: Remove duplicates from a stack using arrays

C++ Stack: Exercise-12 with Solution

Write a C++ program to remove duplicates from a stack using arrays.

Test Data:
Input some elements onto the stack:
Stack elements are: 5 2 2 4 7
Remove duplicates from the said stack:
Stack elements are: 5 2 4 7

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 overflow" << 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;
    }

    // Function to remove duplicates from the stack
    void remove_duplicates(Stack& stk);
};

void Stack::remove_duplicates(Stack& stk) {
    if (stk.isEmpty()) {
        cout << "Stack is empty." << endl; // Display message if the stack is empty
        return;
    }

    int size = stk.top + 1; // Get the size of the stack
    int temp[size]; // Create a temporary array to store stack elements
    int count = 0; // Initialize count to 0

    // The stack elements are copied into a temporary array
    while (!stk.isEmpty()) {
        temp[count++] = stk.pop(); // Pop elements from stack and store in temporary array
    }

    // Remove duplicates from the temporary array
    for (int i = 0; i < count; i++) {
        for (int j = i + 1; j < count; j++) {
            if (temp[i] == temp[j]) {
                // Duplicate elements are marked with -1
                temp[j] = -1;
            }
        }
    }

    // Non-duplicate elements are pushed back onto the stack
    for (int i = count - 1; i >= 0; i--) {
        if (temp[i] != -1) {
            stk.push(temp[i]); // Push non-duplicate elements back onto the original stack
        }
    }
}

int main() {
    Stack stk; 
    cout << "Input some elements onto the stack:";
    stk.push(7);
    stk.push(4);
    stk.push(2);
    stk.push(2);
    stk.push(5);
    stk.display();
    cout << "\nRemove duplicates from the said stack:";
    stk.remove_duplicates(stk); // Remove duplicates from the stack
    stk.display();
    cout << "\nInput two more elements onto the stack:";
    stk.push(7);
    stk.push(5);
    stk.display();
    cout << "\nRemove duplicates from the said stack:";
    stk.remove_duplicates(stk); // Remove duplicates from the stack
    stk.display();
    cout << endl;
}

Sample Output:

Input some elements onto the stack:
Stack elements are: 5 2 2 4 7

Remove duplicates from the said stack:
Stack elements are: 5 2 4 7

Input two more elements onto the stack:
Stack elements are: 5 7 5 2 4 7

Remove duplicates from the said stack:
Stack elements are: 5 7 2 4

Flowchart:

CPP Code Editor:

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Previous C++ Exercise: Find and remove the lowest element in a stack.
Next C++ Exercise: Delete all occurrences of an item in a stack.