function add(a, b) {
  return a + b;
}

function subtract(a, b) {
  return a - b;
}

function sum(array) {
  return array.reduce((current, total) => total + current, 0);
}

function multiply(array) {
    return array.length
      ? array.reduce((accumulator, nextItem) => accumulator * nextItem)
      : 0;
}

function power(a, b) {
  return Math.pow(a, b);
}

function factorial(n) {
  if (n === 0) {return 1};
  return n * factorial(n -1)	
}

module.exports = {
	add,
	subtract,
	sum,
	multiply,
    power,
	factorial
}