Substring primes: Difference between revisions
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<pre>
[2, 3, 5, 7, 23, 37, 53, 73, 373]
</pre>
=== Advanced task ===
<lang julia>using Primes
const nt, nons = [0], Int[]
counted_primetest(n) = (nt[1] += 1; b = isprime(n); !b && push!(nons, n); b)
# start with 1 digit primes
const results = [2, 3, 5, 7]
# check 2 digit candidates
for n in results, i in [3, 7]
if n != i
candidate = n * 10 + i
candidate < 100 && counted_primetest(candidate) && push!(results, candidate)
end
end
# check 3 digit candidates
for n in results, i in [3, 7]
if 10 < n < 100 && n % 10 != i
candidate = n * 10 + i
counted_primetest(candidate) && push!(results, candidate)
end
end
println("Results: $results.\nThe function isprime() was called $(nt[1]) times.")
println("Discarded candidates: ", nons)
# Because 237, 537, and 737 are already excluded, we cannot generate any larger candidates from 373.
</lang>{{out}}
<pre>
Results: [2, 3, 5, 7, 23, 37, 53, 73, 373].
The function isprime() was called 10 times.
Discarded candidates: [27, 57, 237, 537, 737]
</pre>
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