all tasks

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

@@ -0,0 +1,34 @@
+def merge_sort(m)
+    if m.length <= 1
+        return m
+    end
+
+    middle = m.length / 2
+    left = m[0,middle]
+    right = m[middle..-1]
+
+    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
+    end
+
+    unless left.empty?
+        result += left
+    end
+    unless right.empty?
+        result += right
+    end
+    result
+end

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

@@ -0,0 +1,36 @@
+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
+  end
+
+  protected
+  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)
+    end
+  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]
+
+ary = [["UK", "London"], ["US", "New York"], ["US", "Birmingham"], ["UK", "Birmingham"]]
+ary.mergesort {|a, b| a[1] <=> b[1]}
+# => [["US", "Birmingham"], ["UK", "Birmingham"], ["UK", "London"], ["US", "New York"]]