Adding Tuplets functions to generate all n-tuplets (pairs, triplets e…

…tc) (#67)

* Adding Tuplets functions to generate all n-tuplets (pairs, triplets etc)

* lint fix plus tweak the 0 case

Makefile

@@ -0,0 +1,8 @@
+
+lint: .golangci.yml
+	golangci-lint run
+
+.golangci.yml: Makefile
+	curl -fsS -o .golangci.yml https://raw.githubusercontent.com/fortio/workflows/main/golangci.yml
+
+.PHONY: lint

sets.go

@@ -226,3 +226,28 @@ func Sort[Q constraints.Ordered](s Set[Q]) []Q {
 	slices.Sort(keys)
 	return keys
 }
+
+// Tuplets generates all the combinations of N of elements of the set.
+// for n = 2, it would return all pairs of elements.
+// for n = 3, all triplets, etc.
+func Tuplets[Q constraints.Ordered](s Set[Q], n int) [][]Q {
+	if n == 0 {
+		return [][]Q{}
+	}
+	if n == 1 {
+		res := make([][]Q, s.Len())
+		for i, e := range Sort(s) {
+			v := []Q{e}
+			res[i] = v
+		}
+		return res
+	}
+	res := make([][]Q, 0)
+	for _, e := range Sort(s) {
+		t := s.Clone()
+		for _, sub := range Tuplets(t.Minus(New(e)), n-1) {
+			res = append(res, append([]Q{e}, sub...))
+		}
+	}
+	return res
+}

sets_test.go

@@ -157,12 +157,31 @@ func TestNonOrderedJSON(t *testing.T) {
 	// though I guess given it could be in any order it could be accidentally sorted too
 	assert.NotEqual(t, `[{"X":1},{"X":2},{"X":3},{"X":4}]`, string(b))
 	u := sets.New[foo]()
-	json.Unmarshal(b, &u)
+	err = json.Unmarshal(b, &u)
 	assert.NoError(t, err)
 	assert.Equal(t, 4, u.Len())
 	assert.True(t, s.Equals(u))
 }
 
+func TestGenerate(t *testing.T) {
+	setA := sets.New("a", "b", "c")
+	res := sets.Tuplets(setA, 0)
+	assert.Equal(t, res, [][]string{}, "should match empty")
+	res = sets.Tuplets(setA, 1)
+	assert.Equal(t, res, [][]string{{"a"}, {"b"}, {"c"}}, "should match single/identical")
+	res = sets.Tuplets(setA, 2)
+	assert.Equal(t, res, [][]string{{"a", "b"}, {"a", "c"}, {"b", "a"}, {"b", "c"}, {"c", "a"}, {"c", "b"}}, "should match pairs")
+	res = sets.Tuplets(setA, 3)
+	assert.Equal(t, res, [][]string{
+		{"a", "b", "c"},
+		{"a", "c", "b"},
+		{"b", "a", "c"},
+		{"b", "c", "a"},
+		{"c", "a", "b"},
+		{"c", "b", "a"},
+	}, "should match triplets")
+}
+
 func TestBadJson(t *testing.T) {
 	jsonStr := `[
 		"a,b",