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 \'trian         


        

Answer 1

Here is what I wrote and it all worked fine.

def triangle(a, b, c)
  # WRITE THIS CODE
  raise TriangleError, "Sides have to be greater than zero" if (a == 0) | (b == 0) | (c == 0)
  raise TriangleError, "Sides have to be a postive number" if (a < 0) | (b < 0) | (c < 0)
  raise TriangleError, "Two sides can never be less than the sum of one side" if ((a + b) < c) | ((a + c) < b) | ((b + c) < a)
  raise TriangleError, "Two sides can never be equal one side" if ((a + b) ==  c) | ((a + c) ==  b) | ((b + c) ==  a)
  return :equilateral if (a == b) & (a == c) & (b == c)
  return :isosceles if (a == b) | (a == c) | (b == c)
  return :scalene

end

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

Answer 2

  #(1)Any zero or -ve values
  if [a,b,c].any? { |side_length| side_length <= 0 }
    raise TriangleError
  end

  #(2)Any side of a triangle must be less than the sum of the other two sides
  # a <  b+c, b <  a+c  and c <  a+b  a  valid   triangle
  # a >= b+c, b >= a+c  and c >= a+b  an invalid triangle

  total_of_side_lengths = [a,b,c].inject {|total,x| total += x}

  if [a,b,c].any? { |side_length| side_length >= (total_of_side_lengths - side_length)}
    raise TriangleError
  end

Answer 3

After try to understand what I must to do with koan 151, I got it with the first posts, and get lot fun to check everyone solution :) ... here is the mine:

def triangle(a, b, c)
  array = [a, b, c].sort
  raise TriangleError if array.min <= 0 || array[0]+array[1] <= array[2]
  array.uniq!
  array.length == 1 ? :equilateral: array.length == 2 ? :isosceles : :scalene
end

Koan is a very interesting way to learn Ruby

Answer 4

You could also try to instance the exception with:

raise TriangleError.new("All sides must be greater than 0") if a * b * c <= 0

Answer 5

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 6

I ended up with this code:

def triangle(a, b, c)
    raise TriangleError, "impossible triangle" if [a,b,c].min <= 0
    x, y, z = [a,b,c].sort
    raise TriangleError, "no two sides can be < than the third" if x + y <= z

    if a == b && b == c # && a == c # XXX: last check implied by previous 2
        :equilateral
    elsif a == b || b == c || c == a
        :isosceles
    else
        :scalene
    end
end 

I don't like the second condition/raise, but I'm unsure how to improve it further.