Add trinary exercise

assignments/ruby/trinary/example.rb

@@ -0,0 +1,17 @@
+class Trinary
+
+  BASE = 3
+
+  attr_reader :digits
+  def initialize(decimal)
+    @digits = decimal.reverse.chars.collect(&:to_i)
+  end
+
+  def to_decimal
+    decimal = 0
+    digits.each_with_index do |digit, index|
+      decimal += digit * BASE**index
+    end
+    decimal
+  end
+end

assignments/ruby/trinary/test.rb

@@ -0,0 +1,49 @@
+require 'minitest/autorun'
+require 'minitest/pride'
+require_relative 'trinary'
+
+class TrinaryTest < MiniTest::Unit::TestCase
+  def test_trinary_1_is_decimal_1
+    assert_equal 1, Trinary.new("1").to_decimal
+  end
+
+  def test_trinary_2_is_decimal_2
+    skip
+    assert_equal 2, Trinary.new("2").to_decimal
+  end
+
+  def test_trinary_10_is_decimal_3
+    skip
+    assert_equal 3, Trinary.new("10").to_decimal
+  end
+
+  def test_trinary_11_is_decimal_4
+    skip
+    assert_equal 4, Trinary.new("11").to_decimal
+  end
+
+  def test_trinary_100_is_decimal_9
+    skip
+    assert_equal 9, Trinary.new("100").to_decimal
+  end
+
+  def test_trinary_112_is_decimal_14
+    skip
+    assert_equal 14, Trinary.new("112").to_decimal
+  end
+
+  def test_trinary_222_is_26
+    skip
+    assert_equal 26, Trinary.new("222").to_decimal
+  end
+
+  def test_trinary_1122000120_is_32091
+    skip
+    assert_equal 32091, Trinary.new("1122000120").to_decimal
+  end
+
+  def test_invalid_trinary_is_decimal_0
+    skip
+    assert_equal 0, Trinary.new("carrot").to_decimal
+  end
+end

assignments/shared/trinary.md

@@ -0,0 +1,23 @@
+The program should consider strings specifying an invalid trinary as the value 0.
+
+Trinary numbers contain three symbols: 0, 1, and 2.
+
+The last place in a trinary number is the 1's place. The second to last is the 3's place, the third to last is the 9's place, etc.
+
+```bash
+# "102012"
+    1       0       2       0       1       2    # the number
+1*3^5 + 0*3^4 + 2*3^3 + 0*3^3 + 1*3^1 + 2*3^0    # the value
+  243 +     0 +    54 +     0 +     3 +     2 =  302
+```
+
+If you want to write extra tests and/or check your answers, feel free to use irb:
+
+```ruby
+irb(main):001:0> 302.to_s(3)
+=> "102012"
+irb(main):002:0> 81.to_s(3)
+=> "10000"
+irb(main):003:0> 91.to_s(3)
+=> "10101"
+```

assignments/shared/trinary.yml

@@ -0,0 +1,4 @@
+---
+blurb: "Write a program that will convert a trinary number, represented as a string (i.e. '102012'), to it's decimal equivalent using first principles."
+source: "All of Computer Science"
+source_url: "http://www.wolframalpha.com/input/?i=binary&a=*C.binary-_*MathWorld-"

lib/exercism.rb

@@ -34,7 +34,7 @@ def self.current_curriculum
         grade-school robot-name leap etl space-age grains
         gigasecond triangle scrabble-score roman-numerals
         binary prime-factors raindrops allergies strain
-        atbash-cipher accumulate crypto-square
+        atbash-cipher accumulate crypto-square trinary
       )
       @curriculum.add(rb, rb_slugs)