Java: N^th element from the top of the stack

Java Stack: Exercise-15 with Solution

Write a Java program to get the nth element from the top of the 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;
  }

  public int getNthElementFromTop(int n) {
    if (top - n + 1 < 0) {
      System.out.println("Invalid value of n");
      return -1;
    } else {
      return arr[top - n + 1];
    }
  }

  // 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) {
    System.out.println("Initialize a stack:");
    Stack stack = new Stack(5);
    System.out.println("Input some elements on the stack:");
    stack.push(1);
    stack.push(2);
    stack.push(3);
    stack.push(4);
    stack.push(5);
    stack.display();
    int n = stack.getNthElementFromTop(2);
    System.out.println("\nThe 2nd element from the top is " + n);
    n = stack.getNthElementFromTop(3);
    System.out.println("\nThe 3rd element from the top is " + n);
    n = stack.getNthElementFromTop(4);
    System.out.println("\nThe 4th element from the top is " + n);

  }
}

Sample Output:

Initialize a stack:
Input some elements on the stack:
Stack elements: 5 4 3 2 1

The 2nd element from the top is 4

The 3rd element from the top is 3

The 4th element from the top is 2

Flowchart:

Live Demo:

Java Code Editor:

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