new file: sets/stringsUnionFind.go

2026-07-18 17:34:33 -04:00
parent e54607e9ed
commit 8c73d121e4
3 changed files with 266 additions and 3 deletions
@@ -0,0 +1,65 @@
+package sets
+
+// NamedUnionFind{
+// unionFind *UnionFind
+// index     map[string]int
+// names     []string
+// }
+type NamedUnionFind struct {
+	unionFind *UnionFind
+	index     map[string]int
+	names     []string
+}
+
+// NewStringsUnion() -> creates a disjoint set from a slice of strings,
+// the constructor will deduplicate and return a NamedUnionFind
+func NewStringsUnion(params []string) *NamedUnionFind {
+	namedUnion := &NamedUnionFind{
+		index: make(map[string]int, len(params)),
+	}
+
+	for _, name := range params {
+		if _, seen := namedUnion.index[name]; !seen {
+			namedUnion.index[name] = len(namedUnion.names)
+			namedUnion.names = append(namedUnion.names, name)
+		}
+	}
+
+	namedUnion.unionFind = NewUnionFind(len(namedUnion.names))
+
+	return namedUnion
+}
+
+// Union() -> creates an Union of 2 values, returns true if success
+func (n *NamedUnionFind) Union(a, b string) bool {
+	paramA, ok1 := n.index[a]
+	paramB, ok2 := n.index[b]
+	if !ok1 || !ok2 {
+		return false
+	}
+	return n.unionFind.Union(paramA, paramB)
+}
+
+// IsUnion() -> returns true if the parameters have the same root
+func (n *NamedUnionFind) IsUnion(a, b string) bool {
+	paramA, ok1 := n.index[a]
+	paramB, ok2 := n.index[b]
+	if !ok1 || !ok2 {
+		return false
+	}
+	return n.unionFind.IsUnion(paramA, paramB)
+}
+
+// Rep() -> returns the representative name of  group, and false if the name is unknown.
+func (n *NamedUnionFind) Rep(a string) (string, bool) {
+	ia, ok := n.index[a]
+	if !ok {
+		return "", false
+	}
+	return n.names[n.unionFind.Find(ia)], true
+}
+
+// Disjointed() -> returns the count of disjointed sets remaining
+func (n *NamedUnionFind) Disjointed() int {
+	return n.unionFind.Disjointed()
+}
@@ -1,12 +1,17 @@
 package sets

+//	UnionFind {
+//		disjointed int
+//		parent     []int
+//		rank       []int
+//	}
 type UnionFind struct {
 	disjointed int
 	parent     []int
 	rank       []int
 }

-// NewUnionFind() -> Creates an disjoint set
+// NewUnionFind() -> Creates an disjoint set ,takes the unique elements as parameter.
 func NewUnionFind(uniqueElements int) *UnionFind {
 	// counts from 0 correction
 	uniqueElements += 1
@@ -68,7 +73,7 @@ func (uf *UnionFind) Union(a int, b int) bool {
 }

 // IsUnion() -> returns true if the parameters have the same root
-func (uf UnionFind) IsUnion(a int, b int) bool {
+func (uf *UnionFind) IsUnion(a int, b int) bool {
 	if uf.Find(a) == uf.Find(b) {
 		return true
 	}
@@ -76,6 +81,6 @@ func (uf UnionFind) IsUnion(a int, b int) bool {
 }

 // Disjointed() -> returns the count of disjointed sets remaining
-func (uf UnionFind) Disjointed() int {
+func (uf *UnionFind) Disjointed() int {
 	return uf.disjointed
 }
@@ -0,0 +1,193 @@
+package tests
+
+import (
+	"testing"
+
+	"datastructures/sets"
+)
+
+// --- NewStringsUnion ---
+
+func TestNewStringsUnionStartsFullyDisjointed(t *testing.T) {
+	u := sets.NewStringsUnion([]string{"a", "b", "c", "d"})
+	if got := u.Disjointed(); got != 4 {
+		t.Errorf("expected 4 disjoint sets initially, got %d", got)
+	}
+}
+
+func TestNewStringsUnionDeduplicates(t *testing.T) {
+	u := sets.NewStringsUnion([]string{"a", "b", "a", "c", "b", "a"})
+	// only a, b, c are unique
+	if got := u.Disjointed(); got != 3 {
+		t.Errorf("expected 3 disjoint sets after dedup, got %d", got)
+	}
+}
+
+func TestNewStringsUnionEachNameIsOwnRep(t *testing.T) {
+	names := []string{"alice", "bob", "carol"}
+	u := sets.NewStringsUnion(names)
+	for _, name := range names {
+		rep, ok := u.Rep(name)
+		if !ok {
+			t.Errorf("expected %q to be known", name)
+		}
+		if rep != name {
+			t.Errorf("expected %q to be its own representative, got %q", name, rep)
+		}
+	}
+}
+
+func TestNewStringsUnionEmptyInput(t *testing.T) {
+	u := sets.NewStringsUnion(nil)
+	if got := u.Disjointed(); got != 0 {
+		t.Errorf("expected 0 disjoint sets for empty input, got %d", got)
+	}
+}
+
+// --- Union ---
+
+func TestNamedUnionReturnsTrueOnMerge(t *testing.T) {
+	u := sets.NewStringsUnion([]string{"a", "b", "c"})
+	if !u.Union("a", "b") {
+		t.Error("expected Union(a,b) to return true on a fresh merge")
+	}
+}
+
+func TestNamedUnionReturnsFalseWhenAlreadyJoined(t *testing.T) {
+	u := sets.NewStringsUnion([]string{"a", "b", "c"})
+	u.Union("a", "b")
+	if u.Union("a", "b") {
+		t.Error("expected Union(a,b) to return false when already in the same set")
+	}
+}
+
+func TestNamedUnionReturnsFalseTransitively(t *testing.T) {
+	u := sets.NewStringsUnion([]string{"a", "b", "c"})
+	u.Union("a", "b")
+	u.Union("b", "c")
+	// a and c are now connected through b
+	if u.Union("a", "c") {
+		t.Error("expected Union(a,c) to return false (connected via b)")
+	}
+}
+
+func TestNamedUnionUnknownNameReturnsFalse(t *testing.T) {
+	u := sets.NewStringsUnion([]string{"a", "b"})
+	if u.Union("a", "ghost") {
+		t.Error("expected Union with an unknown name to return false")
+	}
+	// the unknown name must not have silently merged anything
+	if got := u.Disjointed(); got != 2 {
+		t.Errorf("expected the count to stay at 2 after a failed union, got %d", got)
+	}
+}
+
+func TestNamedUnionDecrementsDisjointedCount(t *testing.T) {
+	u := sets.NewStringsUnion([]string{"a", "b", "c", "d"})
+	u.Union("a", "b") // 4 -> 3
+	u.Union("c", "d") // 3 -> 2
+	if got := u.Disjointed(); got != 2 {
+		t.Errorf("expected 2 disjoint sets, got %d", got)
+	}
+}
+
+func TestNamedUnionIsSymmetric(t *testing.T) {
+	u := sets.NewStringsUnion([]string{"a", "b"})
+	u.Union("b", "a")
+	if !u.IsUnion("a", "b") {
+		t.Error("expected Union(b,a) to connect a and b regardless of argument order")
+	}
+}
+
+// --- IsUnion ---
+
+func TestNamedIsUnionTrueAfterMerge(t *testing.T) {
+	u := sets.NewStringsUnion([]string{"a", "b", "c"})
+	u.Union("a", "b")
+	if !u.IsUnion("a", "b") {
+		t.Error("expected a and b to be in the same set after Union")
+	}
+}
+
+func TestNamedIsUnionTransitive(t *testing.T) {
+	u := sets.NewStringsUnion([]string{"a", "b", "c", "d"})
+	u.Union("a", "b")
+	u.Union("b", "c")
+	if !u.IsUnion("a", "c") {
+		t.Error("expected a and c to be connected through b")
+	}
+	if u.IsUnion("a", "d") {
+		t.Error("expected d to remain disjoint from the {a,b,c} set")
+	}
+}
+
+func TestNamedIsUnionUnknownNameReturnsFalse(t *testing.T) {
+	u := sets.NewStringsUnion([]string{"a", "b"})
+	if u.IsUnion("a", "ghost") {
+		t.Error("expected IsUnion with an unknown name to return false")
+	}
+}
+
+// --- Rep ---
+
+func TestRepIsSharedAfterUnion(t *testing.T) {
+	u := sets.NewStringsUnion([]string{"a", "b", "c"})
+	u.Union("a", "b")
+	u.Union("b", "c")
+
+	repA, _ := u.Rep("a")
+	repB, _ := u.Rep("b")
+	repC, _ := u.Rep("c")
+	if repA != repB || repB != repC {
+		t.Errorf("expected a, b, c to share one representative, got %q %q %q", repA, repB, repC)
+	}
+}
+
+func TestRepUnknownNameReturnsFalse(t *testing.T) {
+	u := sets.NewStringsUnion([]string{"a", "b"})
+	if rep, ok := u.Rep("ghost"); ok || rep != "" {
+		t.Errorf("expected (\"\", false) for an unknown name, got (%q, %v)", rep, ok)
+	}
+}
+
+func TestRepDistinctForSeparateSets(t *testing.T) {
+	u := sets.NewStringsUnion([]string{"a", "b", "c", "d"})
+	u.Union("a", "b")
+	u.Union("c", "d")
+
+	repA, _ := u.Rep("a")
+	repC, _ := u.Rep("c")
+	if repA == repC {
+		t.Errorf("expected separate sets to have different representatives, both were %q", repA)
+	}
+}
+
+// --- Scenario: grouping people into friend circles ---
+
+func TestFriendCircles(t *testing.T) {
+	friendships := [][2]string{
+		{"alice", "bob"}, {"bob", "carol"}, // circle A: alice-bob-carol
+		{"dave", "erin"},                    // circle B: dave-erin
+		{"frank", "grace"}, {"grace", "frank"}, // circle C: frank-grace (redundant)
+	}
+
+	circles := sets.NewStringsUnion([]string{
+		"alice", "bob", "carol", "dave", "erin", "frank", "grace",
+	})
+	for _, f := range friendships {
+		circles.Union(f[0], f[1])
+	}
+
+	if got := circles.Disjointed(); got != 3 {
+		t.Errorf("expected 3 friend circles, got %d", got)
+	}
+	if !circles.IsUnion("alice", "carol") {
+		t.Error("expected alice and carol to be in the same circle")
+	}
+	if circles.IsUnion("alice", "dave") {
+		t.Error("expected alice (circle A) and dave (circle B) to be in different circles")
+	}
+	if !circles.IsUnion("frank", "grace") {
+		t.Error("expected frank and grace to be in the same circle despite the redundant link")
+	}
+}