re: Daily Challenge #7 - Factorial Decomposition VIEW POST

FULL DISCUSSION
 
function decompose(n) {
  if (typeof(n) !== 'number')
    throw new Error('must be an integer');
  const factorial = getFactorial(n);
  const factors = factorize(factorial);
  const factorFrequencyArray = parseFactors(factors);
  const formattedStr = stringify(factorFrequencyArray);
  return formattedStr;
}
function stringify(exponents) {
  let str = '';
  let i = 0;
  exponents.forEach(exponent => {
    if (exponents[i] === 1)
      str += `${i} * `;
    else if (exponents[i] !== 0)
      str += `${i}^${exponents[i]} * `;
    i++;
  });
  return str.substring(0, str.length - 3);
}
// O(n)
function getFactorial(n) {
    let factorial = 1n;
    for(let i = 1n; i <= n; i ++)
      factorial *= i;
    return factorial;
  }
// O(n)
function parseFactors(factors) {
  let exponents = Array(57).fill(0);
  factors.forEach(factor => exponents[factor]++);
  return exponents;
}
// O(log(n))
function factorize(n) {
  const primes = [2n,3n,5n,7n,11n,13n,17n,19n,23n,29n,
  31n,37n,43n,47n,53n,59n,61n,67n,71n,73n,79n,83n,89n,97n];
  let primeIndex = 0;
  let factors = [];
  while(!primes.includes(n)) {
    if (n % primes[primeIndex] === 0n) {
      factors.push(primes[primeIndex]);
      n = n / primes[primeIndex];
      primeIndex = 0;
    } 
    else 
      primeIndex++;
  }
  factors.push(n);
  return factors;
}
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