euler-3.rb

   1 #!/usr/bin/ruby -w
   2
   3 require 'primes.rb'
   4
   5 if ARGV[0].to_i != 0
   6   $TARGET = ARGV[0].to_i
   7 else
   8   $TARGET = 600851475143
   9 end
  10
  11 primes = Primes.instance
  12
  13 quotient = $TARGET
  14 prime_factors = []
  15 prime_index = 0
  16
  17 while quotient > 1
  18 # puts "trying factor #{primes[prime_index]} with quotient #{quotient}"
  19   if (quotient % primes[prime_index]) == 0
  20     prime_factors << primes[prime_index]
  21     quotient = quotient.div primes[prime_index]
  22   else
  23     prime_index += 1
  24   end
  25 end
  26
  27 if __FILE__==$0
  28   puts "Prime factors of #{$TARGET} are #{prime_factors.join(', ')}; largest is #{prime_factors.max}"
  29 end
  30