Project Euler Problem4
Rubyによる方法
def palindromic_number(n, a=0) if n == 0 a else q, r = n.divmod 10 palindromic_number(q, a * 10 + r) end end def is_palindromic_number(n) n == palindromic_number(n) end largest_palindromic_number = 0 999.downto(100) { |a| 999.downto(a) { |b| c = a * b if c < largest_palindromic_number break end if is_palindromic_number(c) if c > largest_palindromic_number largest_palindromic_number = c end end } } puts largest_palindromic_number