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

You don't need to modify the Exception. Something like this should work;

def triangle(*args)
  args.sort!
  raise TriangleError if args[0] + args[1] <= args[2] || args[0] <= 0
  [nil, :equilateral, :isosceles, :scalene][args.uniq.length]
end

Answer 2

In fact in the following code the condition a <= 0 is redundant. a + b will always be less than c if a < 0 and we know that b < c

    raise TriangleError if a <= 0 || a + b <= c

Answer 3

Here is my version... :-)

def triangle(a, b, c)

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

  if a + b <= c  || a + c <= b ||  b + c <= a
    raise TriangleError
  end 

  return :equilateral if a == b && b == c
  return :isosceles   if a == b || a == c ||  b == c
  return :scalene     if a != b && a != c &&  b != c 

end

Answer 4

Rules:

1. size must be > 0

2. Total of any 2 sides, must be bigger that the 3rd

Code:

raise TriangleError if ( [a,b,c].any? {|x| (x <= 0)} ) or ( ((a+b)<=c) or ((b+c)<=a) or ((a+c)<=b))
[:equilateral, :isosceles, :scalene].fetch([a,b,c].uniq.size - 1)

Answer 5

You have to check that the new created triangle don't break the "Triangle inequality". You can ensure this by this little formula.

if !((a-b).abs < c && c < a + b)
  raise TriangleError
end

When you get the Error:

<TriangleError> exception expected but none was thrown.

Your code is probably throwing an exception while creating a regular triangle in this file. about_triangle_project.rb

Answer 6

Not that this question needed another answer; however, I think this is the simplest and most readable solution. Thanks to all those before me.

def triangle(a, b, c)
  a, b, c = [a, b, c].sort
  raise TriangleError, "all sides must > 0" unless [a, b, c].min > 0
  raise TriangleError, "2 smaller sides together must the > 3rd side" unless a + b > c
  return :equilateral if a == b && a == 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