From f72bc6b98244ebe0af54b9f7bd2323c61e42fba7 Mon Sep 17 00:00:00 2001
From: Aleksander Dudek <aleksander.dudek@ringieraxelspringer.pl>
Date: Mon, 19 Dec 2022 21:48:46 +0100
Subject: [PATCH 1/2] intersection implementation in slices module

---
 go.sum                |  6 ----
 slices/slices.go      | 12 ++++++++
 slices/slices_test.go | 65 +++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 77 insertions(+), 6 deletions(-)

diff --git a/go.sum b/go.sum
index 12890ad84..b00930f70 100644
--- a/go.sum
+++ b/go.sum
@@ -1,14 +1,8 @@
 github.com/google/go-cmp v0.5.8 h1:e6P7q2lk1O+qJJb4BtCQXlK8vWEO8V1ZeuEdJNOqZyg=
 github.com/google/go-cmp v0.5.8/go.mod h1:17dUlkBOakJ0+DkrSSNjCkIjxS6bF9zb3elmeNGIjoY=
-golang.org/x/mod v0.6.0-dev.0.20220419223038-86c51ed26bb4 h1:6zppjxzCulZykYSLyVDYbneBfbaBIQPYMevg0bEwv2s=
-golang.org/x/mod v0.6.0-dev.0.20220419223038-86c51ed26bb4/go.mod h1:jJ57K6gSWd91VN4djpZkiMVwK6gcyfeH4XE8wZrZaV4=
 golang.org/x/mod v0.6.0 h1:b9gGHsz9/HhJ3HF5DHQytPpuwocVTChQJK3AvoLRD5I=
 golang.org/x/mod v0.6.0/go.mod h1:4mET923SAdbXp2ki8ey+zGs1SLqsuM2Y0uvdZR/fUNI=
-golang.org/x/sys v0.0.0-20220722155257-8c9f86f7a55f h1:v4INt8xihDGvnrfjMDVXGxw9wrfxYyCjk0KbXjhR55s=
-golang.org/x/sys v0.0.0-20220722155257-8c9f86f7a55f/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.1.0 h1:kunALQeHf1/185U1i0GOB/fy1IPRDDpuoOOqRReG57U=
 golang.org/x/sys v0.1.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
-golang.org/x/tools v0.1.12 h1:VveCTK38A2rkS8ZqFY25HIDFscX5X9OoEhJd3quQmXU=
-golang.org/x/tools v0.1.12/go.mod h1:hNGJHUnrk76NpqgfD5Aqm5Crs+Hm0VOH/i9J2+nxYbc=
 golang.org/x/tools v0.2.0 h1:G6AHpWxTMGY1KyEYoAQ5WTtIekUUvDNjan3ugu60JvE=
 golang.org/x/tools v0.2.0/go.mod h1:y4OqIKeOV/fWJetJ8bXPU1sEVniLMIyDAZWeHdV+NTA=
diff --git a/slices/slices.go b/slices/slices.go
index cff0cd49e..6f7913772 100644
--- a/slices/slices.go
+++ b/slices/slices.go
@@ -256,3 +256,15 @@ func Grow[S ~[]E, E any](s S, n int) S {
 func Clip[S ~[]E, E any](s S) S {
 	return s[:len(s):len(s)]
 }
+
+// Intersection finds elements that are present in both slices, returning new slice without duplicates
+func Intersection[E comparable](s1, s2 []E) []E {
+	var result []E
+	for i := 0; i < len(s1); i++ {
+		element := s1[i]
+		if Contains(s2, element) && !Contains(result, element) {
+			result = append(result, element)
+		}
+	}
+	return result
+}
diff --git a/slices/slices_test.go b/slices/slices_test.go
index 1d9ffd2f3..106f928ba 100644
--- a/slices/slices_test.go
+++ b/slices/slices_test.go
@@ -767,3 +767,68 @@ func BenchmarkReplace(b *testing.B) {
 	}
 
 }
+
+func TestIntersection(t *testing.T) {
+	intTypeCases := []struct {
+		name string
+		s, v []int
+		want []int
+	}{
+		{
+			name: "empty first slice",
+			s:    []int{},
+			v:    []int{1, 4},
+			want: []int{},
+		},
+		{
+			name: "empty second slice",
+			s:    []int{1, 3},
+			v:    []int{},
+			want: []int{},
+		},
+		{
+			name: "duplicates int",
+			s:    []int{2, 4, 1},
+			v:    []int{1, 3, 1},
+			want: []int{1},
+		},
+		{
+			name: "regular use",
+			s:    []int{1, 2, 3},
+			v:    []int{3, 4, 5},
+			want: []int{3},
+		},
+	}
+	strTypeCases := []struct {
+		name string
+		s, v []string
+		want []string
+	}{
+		{
+			name: "duplicates string",
+			s:    []string{"a", "b", "c"},
+			v:    []string{"b", "b", "z"},
+			want: []string{"b"},
+		},
+		{
+			name: "contain substring",
+			s:    []string{"abc", "h", "i"},
+			v:    []string{"ab", "g", "z"},
+			want: []string{},
+		},
+	}
+	for _, test := range intTypeCases {
+		t.Run(test.name, func(tt *testing.T) {
+			if got := Intersection(test.s, test.v); !Equal(got, test.want) {
+				tt.Errorf("Intersection(%v) = %v, want %v", test.s, got, test.want)
+			}
+		})
+	}
+	for _, test := range strTypeCases {
+		t.Run(test.name, func(tt *testing.T) {
+			if got := Intersection(test.s, test.v); !Equal(got, test.want) {
+				tt.Errorf("Intersection(%v) = %v, want %v", test.s, got, test.want)
+			}
+		})
+	}
+}

From 549e8bfbe3cd3c06fb40d61abb9a557cb4c5122e Mon Sep 17 00:00:00 2001
From: Aleksander Dudek <aleksander.dudek@ringieraxelspringer.pl>
Date: Tue, 20 Dec 2022 07:36:01 +0100
Subject: [PATCH 2/2] performance bust for intersection implementation

---
 slices/slices.go      | 14 ++++++++++++--
 slices/slices_test.go | 12 ++++++++++++
 2 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/slices/slices.go b/slices/slices.go
index 6f7913772..51c9dec61 100644
--- a/slices/slices.go
+++ b/slices/slices.go
@@ -260,9 +260,19 @@ func Clip[S ~[]E, E any](s S) S {
 // Intersection finds elements that are present in both slices, returning new slice without duplicates
 func Intersection[E comparable](s1, s2 []E) []E {
 	var result []E
-	for i := 0; i < len(s1); i++ {
+	s2len := len(s2)
+	s1len := len(s1)
+	if s1len == 0 || s2len == 0 {
+		return result
+	}
+	s2Map := make(map[E]bool, s2len)
+	for i := 0; i < s2len; i++ {
+		el := s2[i]
+		s2Map[el] = true
+	}
+	for i := 0; i < s1len; i++ {
 		element := s1[i]
-		if Contains(s2, element) && !Contains(result, element) {
+		if _, ok := s2Map[element]; ok {
 			result = append(result, element)
 		}
 	}
diff --git a/slices/slices_test.go b/slices/slices_test.go
index 106f928ba..3bb471775 100644
--- a/slices/slices_test.go
+++ b/slices/slices_test.go
@@ -798,6 +798,18 @@ func TestIntersection(t *testing.T) {
 			v:    []int{3, 4, 5},
 			want: []int{3},
 		},
+		{
+			name: "nil value",
+			s:    nil,
+			v:    nil,
+			want: nil,
+		},
+		{
+			name: "different size",
+			s:    []int{1, 5},
+			v:    []int{5, 10, 25},
+			want: []int{5},
+		},
 	}
 	strTypeCases := []struct {
 		name string