Java: Checks if two stacks are equal

Last update on May 09 2025 12:50:15 (UTC/GMT +8 hours)

20. Check if two stacks are equal.

Write a Java program that implements a stack and checks if two stacks are equal.

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 boolean equals(Stack otherStack) {
    if (this.top != otherStack.top) {
      return false;
    }
    for (int i = 0; i <= top; i++) {
      if (this.arr[i] != otherStack.arr[i]) {
        return false;
      }
    }
    return true;
  }
  // 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 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(4);
    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(3);
    System.out.println("\nStack-3");
    stack3.display();
    System.out.println("\nCheck Stack-1 is equal to Stack-2");
    System.out.println(stack1.equals(stack2));
    System.out.println("\nCheck Stack-3 is equal to Stack-1");
    System.out.println(stack3.equals(stack1));
  }
}

Sample Output:

Stack-1
Stack elements: 3 2 1

Stack-2
Stack elements: 6 5 4

Stack-3
Stack elements: 3 2 1

Check Stack-1 is equal to Stack-2
false

Check Stack-3 is equal to Stack-1
true

Flowchart:

For more Practice: Solve these Related Problems:

• Write a Java program to compare two stacks element-by-element for equality using an iterative approach.
• Write a Java program to check if two stacks are equal in content and order by converting them to arrays.
• Write a Java program to implement a recursive method that compares two stacks for equality without modifying them.
• Write a Java program to use Java streams to compare two stacks by zipping their elements and checking for mismatches.

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