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

No Need to change the TriangleError code for either challenge. You just need to check for invalid triangles and raise the error if the triangle isn't.

def triangle(a, b, c)
  if a==0 && b==0 && c==0
    raise TriangleError, "This isn't a triangle"
  end
  if a <0 or b < 0 or c <0
    raise TriangleError, "Negative length - thats not right"
  end
  if a + b <= c  or a + c <= b or  b + c <= a
    raise TriangleError, "One length can't be more (or the same as) than the other two added together.  If it was the same, the whole thing would be a line.  If more, it wouldn't reach. "
  end    
  # WRITE THIS CODE
  if a == b and b == c 
    return :equilateral    
  end      
  if (a==b or b == c or a == c) 
    return :isosceles
  end 
  :scalene      
end

Answer 2

I don't think I see this one here, yet.

I believe all the illegal triangle conditions imply that the longest side can't be more than half the total. i.e:

def triangle(a, b, c)

  fail TriangleError, "Illegal triangle: [#{a}, #{b}, #{c}]" if
    [a, b, c].max >= (a + b + c) / 2.0

  return :equilateral if a == b and b == c
  return :isosceles if a == b or b == c or a == c
  return :scalene

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

This one did take some brain time. But here's my solution

def triangle(a, b, c)
  # WRITE THIS CODE
  raise TriangleError, "All sides must be positive number" if a <= 0 || b <= 0 || c <= 0
  raise TriangleError, "Impossible triangle" if ( a + b + c - ( 2 *  [a,b,c].max ) <= 0  )

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

Answer 5

Here's my solution... honestly I can't think of a more concise and readable one!

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

Answer 6

For the Koan about_triangle_project_2.rb there's no need to change TriangleError class. Insert this code before your triangle algorithm to pass all tests:

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

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