Project Euler: Problem 7: 10001st prime

JavaScript
1

What’s happening:
I don’t know why the code doesn’t seem to work with 10001 on fcc, but using node it does. Someone has any idea of why?
Thanks

My code so far

const nthPrime = (number) => {
  let primes = [2];
  for(let i = 3; primes.length <= number; i+= 2) {
    if(primes.every(v => i % v !== 0)) {
      primes.push(i);
      if(primes.length === number) return i;
    }
  }
}
nthPrime(10001);

My browser information:
User Agent is: Chrome/68.0.3440.84.

Link to the challenge:
https://learn.freecodecamp.org/coding-interview-prep/project-euler/problem-7-10001st-prime

2

The fcc editor thinks that you have a possible infinite loop, so it refuses to run. As far as I know the option to disable that hasn’t been implemented yet

3

Does //noprotect not work anymore or something?

5

Is 100ms a reasonable limit for this question?

Fwiw with the naïve sieve of Eratosthenes you would need an array of over 100000 elements

6

You are totally right, I just optimize the code a bit:

const nthPrime = (number) => {
  let primes = [2];
  let higherDivisorLimit;
  let isPrime;
  for(let i = 3; primes.length < number; i+=2) {
    higherDivisorLimit = Math.sqrt(i) + 1;
    isPrime = true;
    for(let j = 0; primes[j] < higherDivisorLimit; j++) {
      if(i % primes[j] === 0) {
        isPrime = false;
        break;
      }
    }
    if(isPrime) primes.push(i);
  }
  return primes[primes.length - 1];
}
nthPrime(10001);

I just discovered, after reading a bit, I just needed to compare the numbers up to their square root. All divisors higher than that will have a rest equal to a smaller divisor (I think I studied that at primary school, haha).

1 Like
7

Nice. Thanks for sharing your solution. really helped me