examples/euler/prob03.pl

   1 #!/usr/bin/env pugs
   2
   3 # vim: filetype=perl6
   4
   5 =begin Problem
   6 The prime factors of 13195 are 5, 7, 13 and 29.
   7
   8 What is the largest prime factor of the number 317584931803?
   9 =end Problem
  10
  11 use v6;
  12 use Benchmark <timeit>;
  13
  14 sub is_prime($n) {
  15     my @primes = (2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43,
  16         47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97, 101, 103, 107, 109,
  17         113);
  18
  19     return True  if $n == any(@primes);
  20     return False if $n % any(@primes) == 0;
  21     return False if $n % any(2..sqrt($n)) == 0;
  22     return True;
  23 }
  24
  25 sub divide($n) {
  26     my $i = 2;
  27     while $i <= $n {
  28         return ($i, $n / $i) if $n % $i == 0;
  29         $i += 1;
  30     }
  31 }
  32
  33 sub prime_factors($n) {
  34     if is_prime($n) {
  35         ($n);
  36     }
  37     else {
  38         my ($x, $y) = divide($n);
  39         (prime_factors($x), prime_factors($y));
  40     }
  41 }
  42
  43 my @t = timeit(1, -> { say max(prime_factors(317584931803)) });
  44 say "execution time: @t[0]";