Project Euler Problem 32

問題

We shall say that an n-digit number is pandigital if it makes use of all the digits
1 to n exactly once; for example, the 5-digit number, 15234, is 1 through 5 pandigital.

The product 7254 is unusual, as the identity, 39 × 186 = 7254, containing 
multiplicand, multiplier, and product is 1 through 9 pandigital.

Find the sum of all products whose multiplicand/multiplier/product identity can be
written as a 1 through 9 pandigital.

HINT: Some products can be obtained in more than one way so be sure to only include
it once in your sum.

ソース

ans = []
(1..100000).each{|a|
	(1..a).each{|b|
		str = "#{a}#{b}#{a * b}".scan(/./).sort.join
		break if str.size > 10
		ans << a * b if str == "123456789"
	}
}
puts ans.uniq.inject(:+)

解答

45228

感想

コレもそのまま組めば通るが、どこまで繰り返していいかわからず決め打ち（汗
あと、ちゃんと問題を読みましょう！「ヒント」って書いてくれているんだから。。