Java: Remove elements from a stack that do not meet a condition

Java Stack: Exercise-28 with Solution

Write a Java program that implements a stack and create a new stack by removing elements that do not satisfy a condition.

Sample Solution:

Java Code:

import java.util.*;
import java.util.function.Predicate;
import java.util.Arrays;
import java.util.function.IntPredicate;

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;
  }

  // Method to create a new stack by removing elements that do not satisfy a condition
  public Stack filter(Predicate < Integer > predicate) {
    Stack newStack = new Stack(arr.length);

    IntPredicate intPredicate = i -> predicate.test(i);
    int[] filteredArr = Arrays.stream(arr).filter(intPredicate).toArray();

    //int[] filteredArr = Arrays.stream(arr).filter(predicate).toArray();
    for (int i = filteredArr.length - 1; i >= 0; i--) {
      newStack.push(filteredArr[i]);
    }
    return newStack;
  }

  // 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) {
    // Create a stack
    Stack stack = new Stack(5);
    stack.push(1);
    stack.push(2);
    stack.push(3);
    stack.push(4);
    stack.push(5);

    // Define a predicate that tests if the element is even
    Predicate < Integer > isEven = num -> num % 2 == 0;
    // Define a predicate that tests if the element is even
    Predicate < Integer > isOdd = num -> num % 2 != 0;
    // Create a new stack by filtering out odd numbers
    Stack filteredStack1 = stack.filter(isEven);
    // Create a new stack by filtering out even numbers
    Stack filteredStack2 = stack.filter(isOdd);
    // Display the original and filtered stacks
    System.out.println("Original stack:");
    stack.display();
    System.out.println("\nFiltered stack (even numbers only):");
    filteredStack1.display();
    // Display the original and filtered stacks
    System.out.println("\nOriginal stack:");
    stack.display();
    System.out.println("\nFiltered stack (odd numbers only):");
    filteredStack2.display();
  }
}

Sample Output:

Original stack:
Stack elements: 5 4 3 2 1

Filtered stack (even numbers only):
Stack elements: 2 4

Original stack:
Stack elements: 5 4 3 2 1

Filtered stack (odd numbers only):
Stack elements: 1 3 5

Flowchart:

Live Demo:

Java Code Editor:

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