Use Case:

Factorialize a number (n!) to count permutations

First Principles:

• factorials are defined as n! is the product of every positive integer less than or equal to n:

  _n_! = _n_ x (_n_- 1) x (_n_- 2) x (_n_- 3) x ... x 3 x 2 x 1.
  

  Solutions

  Loop method

  const factorial = (num) => {
  if (num <= 0) return 1;
  
  let factNum = 1;
  for(let i = num; i > 0; i--) {
    factNum *= i;
  }
  
  return factNum;
  }
  

  Recursive method

  const factorial = (num) => {
  if (num <= 0) return 1;
  
  return factorial(num - 1) * num;
  }
  

  Why I had to learn this

  Algorithm study