Implemented Stable Marriage in Ruby (#534)

* Implemented Stable Marriage in Ruby

* Update stable_marriage.rb

Author: BjoernAkAManf

CONTRIBUTORS.md

@@ -40,4 +40,5 @@ This file lists everyone, who contributed to this repo and wanted to show up her
 - Thijs Raymakers
 - crafter312
 - Christopher Milan
-- Vexatos
+- Vexatos
+- Björn Heinrichs 

contents/stable_marriage_problem/code/ruby/stable_marriage.rb

@@ -0,0 +1,84 @@
+class Person
+    def initialize(id, name, prefs)
+        @id      = id
+        @name    = name
+        @prefs   = prefs
+        @partner = nil
+        @choices = 0
+    end
+
+    def lonely?
+        @partner.nil?
+    end
+
+    def propose(partners)
+        unless self.lonely?
+            raise '%s is not lonely!' % self.name
+        end
+        choice = @prefs[@choices]
+        partners[choice].onPropose(self)
+        @choices += 1
+    end
+
+    def to_s
+      "#{@name.rjust(20)}: #{self.lonely? && "Lonely" || @partner.name}"
+    end
+
+    def self.generate(size, prefix, r)
+        Array.new(size){|i|
+            Person.new(
+                i,
+                "#{prefix} #{i}",
+                (0 ... size).to_a.shuffle(random: r)
+            )
+        }
+    end
+
+    protected
+    attr_reader :id, :name
+    attr_writer :partner
+
+    # Acts upon a given Proposal
+    def onPropose(partner)
+        unless self.lonely?
+            offer = score(partner)
+            current = score(@partner)
+            return unless offer > current 
+            @partner.partner = nil
+        end
+        @partner = partner
+        partner.partner = self
+    end
+
+    private
+    # Determines the preference of a given partner
+    def score(partner)
+        return 0 if partner.nil?
+        @prefs.size - @prefs.index(partner.id)
+    end
+end
+
+# Deterministic Output, feel free to change seed
+r = Random.new(42)
+
+# Determines Output Columns
+men = Person.generate(4, "Man", r)
+women = Person.generate(4, "Woman", r)
+
+# Assume no Name is longer than 20 characters
+spacer = '-' * (20 * 2 + 2)
+
+# Solve the Problem
+1.step do |round|
+    singles = men.select(&:lonely?)
+    singles.each do |m|
+        m.propose(women)
+    end
+
+    break if singles.empty?
+
+    puts "Round #{round}"
+    puts spacer
+    puts men, women
+    puts spacer
+end

contents/stable_marriage_problem/stable_marriage_problem.md

@@ -29,6 +29,8 @@ Here is a video describing the stable marriage problem:
 ## Example Code
 
 {% method %}
+{% sample lang="ruby" %}
+[import, lang:"ruby"](code/ruby/stable_marriage.rb)
 {% sample lang="jl" %}
 [import, lang:"julia"](code/julia/stable_marriage.jl)
 {% sample lang="py" %}