Java: Top and bottom elements of a stack

Last update on March 11 2025 13:54:51 (UTC/GMT +8 hours)

Write a Java program to find the top and bottom elements of a given stack.

Sample Solution:

Java Code:

import java.util.Scanner;
import java.util.HashSet;

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 remove duplicates
  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) {
    System.out.println("Initialize a stack:");
    Stack stack = new Stack(10);
    System.out.println("\nInput some elements on the stack:");
    stack.push(1);
    stack.push(3);
    stack.push(2);
    stack.push(0);
    stack.push(7);
    stack.push(5);
    stack.push(-1);
    stack.push(3);
    stack.push(-1);
    stack.display();
    System.out.println("\nGet the top element:");
    int top_element = stack.peek();
    System.out.println("Top element: " + top_element);
    System.out.println("\nGet the bottom element:");
    int bottom_element = -1;
    while (!stack.isEmpty()) {
      bottom_element = stack.pop();
    }
    System.out.println("Bottom element: " + bottom_element);
  }
}

Sample Output:

Initialize a stack:

Input some elements on the stack:
Stack elements: -1 3 -1 5 7 0 2 3 1

Get the top element:
Top element: -1

Get the bottom element:
Bottom element: 1

Flowchart:

For more Practice: Solve these Related Problems:

• Write a Java program to retrieve the top element and the bottom element of a stack without modifying it.
• Write a Java program to implement a method that returns both the top and bottom elements of a stack as a pair.
• Write a Java program to traverse a stack iteratively to find the first and last elements, then print them.
• Write a Java program to use recursion to identify and return the top and bottom elements of a stack.

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