Add Union

intersect.go

@@ -94,3 +94,38 @@ func Difference[T comparable](list1 []T, list2 []T) ([]T, []T) {
 
 	return left, right
 }
+
+// Union returns all distinct elements from both collections.
+// result returns will not change the order of elements relatively.
+func Union[T comparable](list1 []T, list2 []T) []T {
+	result := []T{}
+
+	seen := map[T]struct{}{}
+	hasAdd := map[T]struct{}{}
+
+	for _, e := range list1 {
+		seen[e] = struct{}{}
+	}
+
+	for _, e := range list2 {
+		seen[e] = struct{}{}
+	}
+
+	for _, e := range list1 {
+		if _, ok := seen[e]; ok {
+			result = append(result, e)
+			hasAdd[e] = struct{}{}
+		}
+	}
+
+	for _, e := range list2 {
+		if _, ok := hasAdd[e]; ok {
+			continue
+		}
+		if _, ok := seen[e]; ok {
+			result = append(result, e)
+		}
+	}
+
+	return result
+}

intersect_test.go

@@ -93,3 +93,17 @@ func TestDifference(t *testing.T) {
 	is.Equal(left3, []int{})
 	is.Equal(right3, []int{})
 }
+
+func TestUnion(t *testing.T) {
+	is := assert.New(t)
+	result1 := Union[int]([]int{0, 1, 2, 3, 4, 5}, []int{0, 2, 10})
+	result2 := Union[int]([]int{0, 1, 2, 3, 4, 5}, []int{6, 7})
+	result3 := Union[int]([]int{0, 1, 2, 3, 4, 5}, []int{})
+	result4 := Union[int]([]int{0, 1, 2}, []int{0, 1, 2})
+	result5 := Union[int]([]int{}, []int{})
+	is.Equal(result1, []int{0, 1, 2, 3, 4, 5, 10})
+	is.Equal(result2, []int{0, 1, 2, 3, 4, 5, 6, 7})
+	is.Equal(result3, []int{0, 1, 2, 3, 4, 5})
+	is.Equal(result4, []int{0, 1, 2})
+	is.Equal(result5, []int{})
+}