Time for an 2014 update…

Task/Sorting-algorithms-Merge-sort/Ruby/sorting-algorithms-merge-sort-1.rb

@@ -1,34 +1,26 @@
 def merge_sort(m)
-    if m.length <= 1
-        return m
-    end
+  return m if m.length <= 1
 
-    middle = m.length / 2
-    left = m[0,middle]
-    right = m[middle..-1]
+  middle = m.length / 2
+  left = m[0,middle]
+  right = m[middle..-1]
 
-    left = merge_sort(left)
-    right = merge_sort(right)
-    merge(left, right)
+  left = merge_sort(left)
+  right = merge_sort(right)
+  merge(left, right)
 end
 
 def merge(left, right)
-    result = []
-
-    until left.empty? || right.empty?
-        # change the direction of this comparison to change the direction of the sort
-        if left.first <= right.first
-            result << left.shift
-        else
-            result << right.shift
-        end
+  result = []
+  until left.empty? || right.empty?
+    if left.first <= right.first
+      result << left.shift
+    else
+      result << right.shift
     end
-
-    unless left.empty?
-        result += left
-    end
-    unless right.empty?
-        result += right
-    end
-    result
+  end
+  result + left + right
 end
+
+ary = [7,6,5,9,8,4,3,1,2,0]
+p merge_sort(ary)                  # => [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

Task/Sorting-algorithms-Merge-sort/Ruby/sorting-algorithms-merge-sort-2.rb

@@ -1,36 +1,32 @@
 class Array
   def mergesort(&comparitor)
-    if length <= 1
-      self
-    else
-      unless comparitor
-        comparitor = lambda {|a, b| a <=> b}
-      end
-      middle = length / 2
-      left  = self[0,  middle].mergesort(&comparitor)
-      right = self[middle..-1].mergesort(&comparitor)
-      merge(left, right, comparitor)
-    end
+    return self if length <= 1
+    comparitor ||= lambda {|a, b| a <=> b}
+    middle = length / 2
+    left  = self[0,  middle].mergesort(&comparitor)
+    right = self[middle..-1].mergesort(&comparitor)
+    merge(left, right, comparitor)
   end
 
-  protected
+  private
   def merge(left, right, comparitor)
-    if left.empty?
-      right
-    elsif right.empty?
-      left
-    elsif comparitor.call(left.first, right.first) <= 0
-      [left.first] + merge(left[1..-1], right, comparitor)
-    else
-      [right.first] + merge(left, right[1..-1], comparitor)
+    result = []
+    until left.empty? || right.empty?
+      # change the direction of this comparison to change the direction of the sort
+      if comparitor[left.first, right.first] <= 0
+        result << left.shift
+      else
+        result << right.shift
+      end
     end
+    result + left + right
   end
 end
 
 ary = [7,6,5,9,8,4,3,1,2,0]
-ary.mergesort                    # => [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
-ary.mergesort {|a, b| b <=> a}   # => [9, 8, 7, 6, 5, 4, 3, 2, 1, 0]
+p ary.mergesort                    # => [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
+p ary.mergesort {|a, b| b <=> a}   # => [9, 8, 7, 6, 5, 4, 3, 2, 1, 0]
 
 ary = [["UK", "London"], ["US", "New York"], ["US", "Birmingham"], ["UK", "Birmingham"]]
-ary.mergesort {|a, b| a[1] <=> b[1]}
+p ary.mergesort {|a, b| a[1] <=> b[1]}
 # => [["US", "Birmingham"], ["UK", "Birmingham"], ["UK", "London"], ["US", "New York"]]