sellist

from typing import Optional
# optional is used for type hinting when a variable can be of a certain type or None
# i.e. Optional[Item] means the variable can be an Item instance or None, which
# is useful for representing empty slots in the vending machine

# this program can be simplified a lot, but is structured this way to demonstrate
# some object-oriented programming concepts

class Item:

sellist

// The question:
// Some numbers can be made out of a summation of positive consecutive numbers
// Examples:
// 1+2+3 = 6
// 2+3+4 = 9
// 3+4+5+6 = 18
//
// Write a function that takes in an integer and returns a boolean if that number can be made out of a summation of consecutive numbers.
// --------------------------
// First thought was if there was a pattern of numbers that can or cannot be made out of a summation of consecutive numbers

sellist

import java.util.Stack;

class ParenthesesValidator {
    public String parenthesesValidator(String input) {
        Stack<Character> parenStack = new Stack<>();
        char[] inputArray = input.toCharArray();

        for (char c : inputArray) {
            if (c == '(') {
                parenStack.push(c);