ニシキヘビ

ans = []

0.step(10, 0.1) do |x|
  -10.step(0, 0.1) do |y|
    -10.step(10, 0.1) do |z|
      a= x+y-z-2
      b= 3*x+4*y+z-6
      c = 5-(x-2*y+3*z).abs

      if a >0 and b >0 and c >0 then
        ans << 7*x-y+z-4
      end
    end
  end
end

print ans.min

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答え：10.4