Ruby Koans 151 triangle.rb solution

ruby_koans_151_solution.rb

def triangle(a, b, c)
  raise TriangleError if a<=0 or b<=0 or c<=0
  raise TriangleError if a+b<=c or b+c<=a or a+c<=b
  return :equilateral if a==b and a==c                 
  return :isosceles if a==b or b==c or a==c
  :scalene                                                                                                       
end  

I found it helpful to start with:

a, b, c = [a, b, c].sort

This simplifies matters quite a bit:

raise TriangleError unless a > 0
raise TriangleError unless a + b > c
return :equilateral if a == c
return :isosceles if a == b or b == c
:scalene

Nice, that's smart.

I threw the arguments into an array to use the "uniq" method in helping find how many unique sides.

sides = []
sides << a << b << c
sorted_sides = sides.sort
unique_sides = sides.uniq.length
raise TriangleError unless sorted_sides.first > 0
raise TriangleError unless sorted_sides.first + sorted_sides.fetch(1) > sorted_sides.last
return :equilateral if unique_sides == 1
return :isosceles if unique_sides == 2
return :scalene


Cool. My effort to condense your solution:

def triangle(a, b,c)
  (a, b, c), uniq_sides = [a, b, c].sort, [a, b, c].uniq.size
  raise TriangleError unless a > 0 and a + b > c
  return :equilateral if uniq_sides == 1
  return :isosceles if uniq_sides == 2
  :scalene
end

I didn't like repeating [a, b, c] and the only one-liner idea I had was:

a, b, c, uniq_sides = [a, b, c].sort.tap { |sides| sides << sides.uniq.size } 

:/

Even better:

def triangle(a, b, c)
  a, b, c = sides = [a, b, c].sort
  raise TriangleError unless a > 0 and a + b > c
  {1 => :equilateral, 2 => :isosceles, 3 => :scalene}[sides.uniq.size]
end

Or even:

def triangle(a, b, c)
  a, b, c = sides = [a, b, c].sort
  raise TriangleError unless a > 0 and a + b > c
  [nil, :equilateral, :isosceles, :scalene][sides.uniq.size]
end

We're really streamlining this little chunk of code. :)

Nice. I get hung up on a tree instead of seeing the forest of refactoring.

I got rid of the nil, but at this rate we might as well rename sides to x. 😔

def triangle(a, b, c)
  a, b, c = sides = [a, b, c].sort
  raise TriangleError unless a > 0 and a + b > c
  [:scalene, :isosceles, :equilateral][-sides.uniq.size]
end

Until next time, team fistbump. 👊

Using a negative index – clever!

Dan & David,

Hi. I'm Rolando. I'm a student at Flatiron School in NYC, and this exchange was super helpful in helping me figure a solution out.

Just wanted to say thanks!

Thanks for all of you guys