Problem 15 (written in Ruby)

(21..40).to_a.inject(1){|r,s| r*=s } / (1..20).to_a.inject(1){|r,s| r*=s }

Problem:
http://odz.sakura.ne.jp/projecteuler/index.php?Problem%2015

単純に40C20だった。

brute-forceバージョン笑↓

X_MAX = 20

Y_MAX = 20
$count = 0
def search(x, y)

  if x == X_MAX and y == Y_MAX then

    $count += 1

    puts "counting #{$count}...." if $count % 100000 == 0

    return

  end
  search(x+1, y) if x < X_MAX

  search(x, y+1) if y < Y_MAX

end
search(0, 0)

puts "Answer = #{$count}"