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| -rwxr-xr-x | challenge-076/jo-37/perl/ch-1.pl | 45 |
1 files changed, 45 insertions, 0 deletions
diff --git a/challenge-076/jo-37/perl/ch-1.pl b/challenge-076/jo-37/perl/ch-1.pl new file mode 100755 index 0000000000..4897dd70c3 --- /dev/null +++ b/challenge-076/jo-37/perl/ch-1.pl @@ -0,0 +1,45 @@ +#!/usr/bin/perl + +use Test2::V0; +use Math::Prime::XS 'is_prime'; +use bigint; + +# The task states: +# "find the minimum number of prime numbers required, whose summation +# gives you $N". +# This does not imply finding specific summands, IMHO. +# +# According to Goldbach's conjecture, every even number greater than two +# can be expressed as the sum of two primes. As there is no exception to +# this rule for $n <= 4e18, it may be considered as valid for this task. +sub num_prime_summands { + my ($n) = @_; # keep @_ + $_[1] = 2; # provide default retcode + + return 0 if $n < 2; # not a sum of primes + return 1 if $n == 2; # 2 is prime + goto &assure if $n % 2 == 0; # Goldbach's conjecture + return 1 if is_prime $n; # $n is prime + return 2 if is_prime $n - 2; # $n - 2 is prime + + $_[1]++; goto &assure; # Else: $n minus any odd prime is even, + # where Goldbach's conjecture is + # applied again. +} + +# Warn about results that cannot be assured. +sub assure { + my ($n, $r) = @_; + warn "The result is not assured!\n" if $n > 4e18; + + $r; +} + + +is num_prime_summands($_->[0]), $_->[1] + foreach [1, 0], [2, 1], [3, 1], [4, 2], [5, 1], [6, 2], [7, 1], + [8, 2], [9, 2], [10, 2], [11, 1], [12, 2], [13, 1], [14, 2], + [15, 2], [16, 2], [17, 1], [18, 2], [19, 1], [20, 2], [21, 2], + [22, 2], [23, 1], [24, 2], [25, 2], [26, 2], [27, 3], [28, 2]; + +done_testing; |