Ruby Koan 151 raising exceptions

Question

I'm going through the ruby koans, I'm on 151 and I just hit a brick wall.

Here is the koan:

# You need to write the triangle method in the file 'triangle.rb'
require 'triangle.rb'

class AboutTriangleProject2 < EdgeCase::Koan
  # The first assignment did not talk about how to handle errors.
  # Let's handle that part now.
  def test_illegal_triangles_throw_exceptions
    assert_raise(TriangleError) do triangle(0, 0, 0) end
    assert_raise(TriangleError) do triangle(3, 4, -5) end
    assert_raise(TriangleError) do triangle(1, 1, 3) end
    assert_raise(TriangleError) do triangle(2, 4, 2) end
 end
end

Then in triangle.rb we have:

def triangle(a, b, c)
  # WRITE THIS CODE
  if a==b && a==c
    return :equilateral
  end
  if (a==b && a!=c) || (a==c && a!=b) || (b==c && b!=a)
    return :isosceles
  end
  if a!=b && a!=c && b!=c
    return :scalene
  end
  if a==0 && b==0 && c==0
    raise new.TriangleError
  end



end

# Error class used in part 2.  No need to change this code.
class TriangleError < StandardError

end

I am beyond confused - any help at all would be much appreciated!

EDIT: To complete this koan, I need to put something in the TriangleError class - but I have no idea what

UPDATE: Here is what the koan karma thing is saying:

<TriangleError> exception expected but none was thrown.

Answer 1

Here is my elegant answer, with a lot of help from the comments above

def triangle(a, b, c)

   test_tri = [a,b,c]

   if test_tri.min <=0
     raise TriangleError
   end

   test_tri.sort!

   if test_tri[0]+ test_tri[1] <= test_tri[2]
     raise TriangleError
   end

   if a == b and b == c
     :equilateral
   elsif a != b and b != c and a != c 
     :scalene   
   else
     :isosceles     
   end
end

Answer 2

You forgot the case when a,b, or c are negative:

def triangle(a, b, c)
  raise TriangleError if [a,b,c].min <= 0
  x, y, z = [a,b,c].sort
  raise TriangleError if x + y <= z
  [:equilateral,:isosceles,:scalene].fetch([a,b,c].uniq.size - 1)
end

Answer 3

There are some absolutely brilliant people on StackOverflow...I'm reminded of that every time I visit :D Just to contribute to the conversation, here's the solution I came up with:

def triangle(a, b, c)
    raise TriangleError if [a,b,c].min <= 0
    x,y,z = [a,b,c].sort
    raise TriangleError if x + y <= z

    equal_sides = 0
    equal_sides +=1 if a == b
    equal_sides +=1 if a == c
    equal_sides +=1 if b == c

    # Note that equal_sides will never be 2.  If it hits 2 
    # of the conditions, it will have to hit all 3 by the law
    # of associativity
    return [:scalene, :isosceles, nil, :equilateral][equal_sides] 
end 

Answer 4

Leon wins on fancy elegance, Benji for his knowledge the Array API. Here's my brute elegant answer:

def triangle(a, b, c)
   [a, b, c].each { | side | raise TriangleError, "Sides must be positive" unless side > 0 }
   raise TriangleError, "Two sides can never be less than or equal to third side" if ((a + b) <= c) | ((a + c) <= b) | ((b + c) <= a)

   return :equilateral if (a == b) && (b == c)
   return :isosceles if (a == b) || (b == c) || (a == c)
   return :scalene
end

Answer 5

No need to write the TriangleError method. It says 'No need to change this code', so I won't change it at all. Stubborn as I am.

4lines shot it, nice nd clean.

    def triangle(a, b, c)
         if(a * b * c <= 0) || (( (a + c)<=b) || ((a + b)<=c)||((b + c)<=a) )
             raise TriangleError else
             return  ((a == b && b == c && a == c)?  :equilateral:(((a == b)||(b == c)||(a == c))?  :isosceles:  :scalene))
         end
    end


# Error class used in part 2.  No need to change this code.
class TriangleError < StandardError
end

Answer 6

You definately do not update the TriangleError class - I am stuck on 152 myself. I think I need to use the pythag theorem here.

def triangle(a, b, c)
  # WRITE THIS CODE

  if a == 0 || b == 0 || c == 0
    raise TriangleError
  end

  # The sum of two sides should be less than the other side
  if((a+b < c) || (a+c < b) || (b+c < a))
    raise TriangleError
  end
  if a==b && b==c
    return :equilateral
  end
  if (a==b && a!=c) || (a==c && a!=b) || (b==c && b!=a)
    return :isosceles
  end
  if(a!=b && a!=c && b!=c)
    return :scalene
  end


end

# Error class used in part 2.  No need to change this code.
class TriangleError < StandardError
end