16 lines
1.1 KiB
Markdown
16 lines
1.1 KiB
Markdown
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This is a relative straightforward problem:
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- First we calculate all primes from `0` to `200 000` with a sieve of Eratosthenes.
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- 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.
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- If we iterate through all the primes and test the divisibility we can calculate the number of *distinct prime*
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- So we check every fourth number (if it has 4 distinct prime factors).
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- If we found one, we test the 7 surrounding numbers for 4 adjacent matches (the first one we print out and exit the program)
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This program is not that fast, even I did multiple performance improvements:
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- We pre-calculate the primes with an sieve of Eratosthenes
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- We generate an easily iterable array of primes
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- We test only every 4th number - this reduces the number of distinct prime factor calculations greatly
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- We early exit the "test 7 surrounding numbers" method, when we reached a point where there can't be a positive result
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But still, it's mostly optimised brute force and not pretty fast.
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