New Union and UnitWith methods for hashset

hashset/hashset.go

@@ -13,6 +13,15 @@ func New[T comparable]() *HashSet[T] {
 	return &HashSet[T]{m: make(map[T]struct{})}
 }
 
+// InitWith creates a new HashSet initialized with vals.
+func InitWith[T comparable](vals ...T) *HashSet[T] {
+	hs := New[T]()
+	for _, v := range vals {
+		hs.Add(v)
+	}
+	return hs
+}
+
 // Add adds a value to the set.
 func (hs *HashSet[T]) Add(val T) {
 	hs.m[val] = struct{}{}
@@ -45,3 +54,15 @@ func (hs *HashSet[T]) All() iter.Seq[T] {
 		}
 	}
 }
+
+// Union returns the set union of hs with other. It creates a new set.
+func (hs *HashSet[T]) Union(other *HashSet[T]) *HashSet[T] {
+	result := New[T]()
+	for v := range hs.m {
+		result.Add(v)
+	}
+	for v := range other.m {
+		result.Add(v)
+	}
+	return result
+}

hashset/hashset_test.go

@@ -5,57 +5,58 @@ import (
 	"testing"
 )
 
+func checkAll(t *testing.T, hs *HashSet[int], wantSorted []int) {
+	t.Helper()
+	if hs.Len() != len(wantSorted) {
+		t.Errorf("got len=%v, want %v", hs.Len(), len(wantSorted))
+	}
+
+	got := slices.Sorted(hs.All())
+	if !slices.Equal(got, wantSorted) {
+		t.Errorf("got %v, want %v", got, wantSorted)
+	}
+}
+
 func TestAll(t *testing.T) {
 	hs := New[int]()
 
-	checkAll := func(wantSorted []int) {
-		t.Helper()
-		if hs.Len() != len(wantSorted) {
-			t.Errorf("got len=%v, want %v", hs.Len(), len(wantSorted))
-		}
-
-		got := slices.Sorted(hs.All())
-		if !slices.Equal(got, wantSorted) {
-			t.Errorf("got %v, want %v", got, wantSorted)
-		}
-	}
-	checkAll([]int{})
+	checkAll(t, hs, []int{})
 	hs.Add(10)
-	checkAll([]int{10})
+	checkAll(t, hs, []int{10})
 
 	hs.Add(20)
 	hs.Add(13)
-	checkAll([]int{10, 13, 20})
+	checkAll(t, hs, []int{10, 13, 20})
 
 	hs.Add(18)
-	checkAll([]int{10, 13, 18, 20})
+	checkAll(t, hs, []int{10, 13, 18, 20})
 
 	hs.Delete(18)
-	checkAll([]int{10, 13, 20})
+	checkAll(t, hs, []int{10, 13, 20})
 	hs.Delete(10)
-	checkAll([]int{13, 20})
+	checkAll(t, hs, []int{13, 20})
 
 	hs.Add(50)
 	hs.Add(5)
-	checkAll([]int{5, 13, 20, 50})
+	checkAll(t, hs, []int{5, 13, 20, 50})
 
 	hs.Add(60)
 	hs.Add(60)
 	hs.Add(60)
-	checkAll([]int{5, 13, 20, 50, 60})
+	checkAll(t, hs, []int{5, 13, 20, 50, 60})
 
 	hs.Delete(60)
 	hs.Delete(60)
 	hs.Delete(60)
-	checkAll([]int{5, 13, 20, 50})
+	checkAll(t, hs, []int{5, 13, 20, 50})
 
 	hs.Delete(50)
 	hs.Delete(20)
 	hs.Delete(5)
-	checkAll([]int{13})
+	checkAll(t, hs, []int{13})
 
 	hs.Delete(13)
-	checkAll([]int{})
+	checkAll(t, hs, []int{})
 }
 
 func TestContains(t *testing.T) {
@@ -94,3 +95,17 @@ func TestContains(t *testing.T) {
 		checkContains(v, false)
 	}
 }
+
+func TestUnion(t *testing.T) {
+	hs1 := InitWith(10, 20, 30, 40)
+	hs2 := InitWith(11, 21, 30, 41)
+
+	u1 := hs1.Union(hs2)
+	checkAll(t, u1, []int{10, 11, 20, 21, 30, 40, 41})
+
+	u2 := hs1.Union(InitWith(20))
+	checkAll(t, u2, []int{10, 20, 30, 40})
+
+	u3 := hs1.Union(InitWith(90))
+	checkAll(t, u3, []int{10, 20, 30, 40, 90})
+}