add - to SortedArray

lib/sorted_containers/sorted_array.rb

@@ -60,6 +60,16 @@ def +(other)
       new_instance
     end
 
+    # Returns a new SortedArray with the values from the difference of the two arrays.
+    #
+    # @param other [SortedArray] The other array to subtract.
+    # @return [SortedArray] The difference of the two arrays.
+    def -(other)
+      new_instance = self.class.new
+      new_instance.update(to_a - other.to_a)
+      new_instance
+    end
+
     # rubocop:disable Metrics/MethodLength
 
     # Adds a value to the sorted array.

spec/sorted_array_spec.rb

@@ -79,6 +79,44 @@
     end
   end
 
+  describe "-" do
+    it "should return the difference of two arrays" do
+      array1 = SortedContainers::SortedArray.new([1, 2, 3, 4, 5])
+      array2 = SortedContainers::SortedArray.new([3, 4, 5, 6, 7])
+      expect((array1 - array2).to_a).to eq([1, 2])
+    end
+
+    it "should return an empty array if there is no difference" do
+      array1 = SortedContainers::SortedArray.new([1, 2, 3, 4, 5])
+      array2 = SortedContainers::SortedArray.new([1, 2, 3, 4, 5])
+      expect((array1 - array2).to_a).to eq([])
+    end
+
+    it "should return the difference of two arrays with duplicates" do
+      array1 = SortedContainers::SortedArray.new([1, 2, 3, 4, 5, 3, 4, 5])
+      array2 = SortedContainers::SortedArray.new([3, 4, 5, 6, 7])
+      expect((array1 - array2).to_a).to eq([1, 2])
+    end
+
+    it "should return an empty array if the first array is empty" do
+      array1 = SortedContainers::SortedArray.new
+      array2 = SortedContainers::SortedArray.new([1, 2, 3, 4, 5])
+      expect((array1 - array2).to_a).to eq([])
+    end
+
+    it "should return an empty array if the second array is empty" do
+      array1 = SortedContainers::SortedArray.new([1, 2, 3, 4, 5])
+      array2 = SortedContainers::SortedArray.new
+      expect((array1 - array2).to_a).to eq([1, 2, 3, 4, 5])
+    end
+
+    it "should return an empty array if both arrays are empty" do
+      array1 = SortedContainers::SortedArray.new
+      array2 = SortedContainers::SortedArray.new
+      expect((array1 - array2).to_a).to eq([])
+    end
+  end
+
   describe "add" do
     it "sorts items after being added in an arbitrary order" do
       array = SortedContainers::SortedArray.new