Hi I am just casually solving some Project Euler problems using Perl.
For problem 3 (https://projecteuler.net/problem=3) I solved it using the code below. The problem is stated in the code comments. The code is single threaded and takes about 5-10 minutes on a standard Intel i5 CPU on a 3 year old Macbook Air. Can PDL make this faster ? No bignums are being used. #!/usr/bin/env perl use strict; use warnings; use POSIX qw(floor); # Problem 3: # The prime factors of 13195 are 5, 7, 13, 29. # What is the largest prime factor of 600851475143 ? my $num = 600851475143; my $m = floor(sqrt($num)); print "max factor limit: $m\n"; # solve using sieve of erastothenes # my @primes = (); my @possible = (2 .. $m); while (@possible) { my $p = shift @possible; @possible = grep { $_ % $p != 0 } @possible; push @primes, $p; print "Remaining: ", scalar(@possible), "\n"; print "Found possible prime factor: $p\n"; } my @factors = grep { $num % $_ == 0 } @primes; if (@factors) { print "Prime Factors of $num: ", join(",", @factors), "\n"; } else { print "$num is prime\n"; }
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