freeCodeCamp Challenge Guide: Problem 77: Prime summations

Problem 77: Prime summations


Solutions

Solution 1 (Click to Show/Hide)
function primeSummations(n) {
  function getSievePrimes(max) {
    const primesMap = new Array(max).fill(true);
    primesMap[0] = false;
    primesMap[1] = false;
    const primes = [];

    for (let i = 2; i < max; i += 2) {
      if (primesMap[i]) {
        primes.push(i);
        for (let j = i * i; j < max; j += i) {
          primesMap[j] = false;
        }
      }
      if (i === 2) {
        i = 1;
      }
    }
    return primes;
  }

  const MAX_NUMBER = 100;
  const primes = getSievePrimes(MAX_NUMBER);

  for (let curNumber = 2; curNumber < MAX_NUMBER; curNumber++) {
    const combinations = new Array(curNumber + 1).fill(0);
    combinations[0] = 1;
    for (let i = 0; i < primes.length; i++) {
      for (let j = primes[i]; j <= curNumber; j++) {
        combinations[j] += combinations[j - primes[i]];
      }
    }
    if (combinations[curNumber] > n) {
      return curNumber;
    }
  }

  return false;
}