1
0
www.mikescher.com/www/statics/euler/Euler_Problem-047_explanation.md

16 lines
1.1 KiB
Markdown
Raw Normal View History

2017-11-08 17:39:50 +01:00
This is a relative straightforward problem:
- First we calculate all primes from `0` to `200 000` with a sieve of Eratosthenes.
- Then we collect all primes side by side together in the top rows, because we only need to iterate through the primes and never actually do a prime test.
- If we iterate through all the primes and test the divisibility we can calculate the number of *distinct prime*
- So we check every fourth number (if it has 4 distinct prime factors).
- If we found one, we test the 7 surrounding numbers for 4 adjacent matches (the first one we print out and exit the program)
This program is not that fast, even I did multiple performance improvements:
- We pre-calculate the primes with an sieve of Eratosthenes
- We generate an easily iterable array of primes
- We test only every 4th number - this reduces the number of distinct prime factor calculations greatly
- We early exit the "test 7 surrounding numbers" method, when we reached a point where there can't be a positive result
But still, it's mostly optimised brute force and not pretty fast.