Project Euler 68

project_euler_68.rb

def project_euler_68
  res = 0
  arr = (1..9).to_a
  arr.combination(5) do |(*inner)|
    s = inner.inject(&:+)
    next unless s % 5 == 0
    t = s.div(5) + 11
    outer = (arr - inner) << 10
    o_min = outer.min
    inner.combination(2) do |a, b|
      next unless a + b + o_min == t
      (inner - [a, b]).permutation(3) do |c, d, e|
        r = [o_min, t-b-c, t-c-d, t-d-e, t-e-a]
        if (outer - r).empty?
          res = [
            res,
            r.zip([a,b,c,d,e],[b,c,d,e,a]).join.to_i,
            r.rotate.reverse.zip([b,a,e,d,c],[a,e,d,c,b]).join.to_i
          ].max
        end
      end
    end
  end
  res
end

if $0 == __FILE__
  p project_euler_68
end