Java: Stack elements in the first but not in the second

Java Stack: Exercise-22 with Solution

Write a Java program that implements a stack and find elements that are in the first stack but not in the second stack.

Sample Solution:

Java Code:

import java.util.Scanner;

public class Stack {
  private int[] arr;
  private int top;

  // Constructor to initialize the stack
  public Stack(int size) {
    arr = new int[size];
    top = -1;
  }

  // Method to push an element onto the stack
  public void push(int num) {
    if (top == arr.length - 1) {
      System.out.println("Stack is full");
    } else {
      top++;
      arr[top] = num;
    }
  }

  // Method to pop an element from the stack
  public int pop() {
    if (top == -1) {
      System.out.println("Stack Underflow");
      return -1;
    } else {
      int poppedElement = arr[top];
      top--;
      return poppedElement;
    }
  }

  // Method to get the top element of the stack
  public int peek() {
    if (top == -1) {
      System.out.println("Stack is empty");
      return -1;
    } else {
      return arr[top];
    }
  }

  // Method to check if the stack is empty
  public boolean isEmpty() {
    return top == -1;
  }

  // Method to get the size of the stack
  public int getSize() {
    return top + 1;
  }

  public Stack findElementsNotInStack(Stack otherStack) {
    Stack resultStack = new Stack(this.arr.length);
    for (int i = 0; i <= this.top; i++) {
      boolean found = false;
      for (int j = 0; j <= otherStack.top; j++) {
        if (this.arr[i] == otherStack.arr[j]) {
          found = true;
          break;
        }
      }
      if (!found) {
        resultStack.push(this.arr[i]);
      }
    }
    return resultStack;
  }
  // Method to display the elements of the stack
  public void display() {
    if (top == -1) {
      System.out.println("Stack is empty!");
    } else {
      System.out.print("Stack elements: ");
      for (int i = top; i >= 0; i--) {
        System.out.print(arr[i] + " ");
      }
      System.out.println();
    }
  }

  public static void main(String[] args) {
    Stack result = new Stack(5);
    Stack stack1 = new Stack(5);
    stack1.push(1);
    stack1.push(2);
    stack1.push(3);
    System.out.println("\nStack-1");
    stack1.display();
    Stack stack2 = new Stack(5);
    stack2.push(3);
    stack2.push(5);
    stack2.push(6);
    System.out.println("\nStack-2");
    stack2.display();
    Stack stack3 = new Stack(5);
    stack3.push(1);
    stack3.push(2);
    stack3.push(4);
    System.out.println("\nStack-3");
    stack3.display();
    System.out.println("\nFind elements that are in the first stack (stack1) but not in the second stack (stack2):");
    result = stack1.findElementsNotInStack(stack2);
    result.display();
    System.out.println("\nFind elements that are in the first stack (stack1) but not in the second stack (stack3):");
    result = stack1.findElementsNotInStack(stack3);
    result.display();
    System.out.println("\nFind elements that are in the first stack (stack3) but not in the second stack (stack2):");
    result = stack3.findElementsNotInStack(stack2);
    result.display();
  }
}

Sample Output:

Stack-1
Stack elements: 3 2 1

Stack-2
Stack elements: 6 5 3

Stack-3
Stack elements: 4 2 1

Find elements that are in the first stack (stack1) but not in the second stack (stack2):
Stack elements: 2 1

Find elements that are in the first stack (stack1) but not in the second stack (stack3):
Stack elements: 3

Find elements that are in the first stack (stack3) but not in the second stack (stack2):
Stack elements: 4 2 1

Flowchart:

Live Demo:

Java Code Editor:

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Java Stack Previous: Find common elements between two stacks.
Java Stack Exercises Next: Elements from two stacks without duplicates.