Project Euler Problem 36
問題
The decimal number, 585 = 1001001001_(2) (binary), is palindromic in both bases. Find the sum of all numbers, less than one million, which are palindromic in base 10 and base 2. (Please note that the palindromic number, in either base, may not include leading zeros.)
ソース
class Integer def to_bi n = self str = "" while n > 0 str += (n % 2).to_s n >>= 1 end str.scan(/./).reverse.join end def palindromic? self.to_s == self.to_s.scan(/./).reverse.join end end max = 1000000 puts (1...max).inject(0){|s, n| s + (n.palindromic? && n.to_bi.to_i.palindromic? ? n : 0) }
解答
872187
感想
回文数の判断は文字列を反転させると簡単だった
特に難しくはない