2021 Day 8

2021/aoc/stringset/stringset.go

@@ -0,0 +1,108 @@
+package stringset
+
+import (
+	"fmt"
+	"sort"
+	"strings"
+)
+
+type StringSet map[string]struct{}
+
+func Slice(vals []string) StringSet {
+	set := make(StringSet)
+	for _, v := range vals {
+		set[v] = struct{}{}
+	}
+	return set
+}
+
+func Runes(v string) StringSet {
+	return Slice(strings.Split(v, ""))
+}
+
+func (s StringSet) String() string {
+	var elts []string
+	for e := range s {
+		elts = append(elts, e)
+	}
+	sort.Strings(elts)
+	return fmt.Sprintf("{%s}", strings.Join(elts, ", "))
+}
+
+func (s StringSet) Only() string {
+	if len(s) > 1 {
+		panic(fmt.Sprintf("too many elements: %s", s))
+	}
+	for v := range s {
+		return v
+	}
+	panic("empty set")
+}
+
+func (s StringSet) Has(elt string) bool {
+	_, ok := s[elt]
+	return ok
+}
+
+func (s StringSet) add(elt string) {
+	s[elt] = struct{}{}
+}
+
+func (s StringSet) Union(t StringSet) StringSet {
+	set := make(StringSet)
+	for a := range s {
+		set.add(a)
+	}
+	for b := range t {
+		set.add(b)
+	}
+	return set
+}
+
+func (s StringSet) Intersect(t StringSet) StringSet {
+	set := make(StringSet)
+	for a := range s {
+		if t.Has(a) {
+			set.add(a)
+		}
+	}
+	return set
+}
+
+func (s StringSet) Minus(t StringSet) StringSet {
+	set := make(StringSet)
+	for a := range s {
+		if !t.Has(a) {
+			set.add(a)
+		}
+	}
+	return set
+}
+
+func (s StringSet) Equal(t StringSet) bool {
+	if len(s) != len(t) {
+		return false
+	}
+	for a := range s {
+		if !t.Has(a) {
+			return false
+		}
+	}
+	return true
+}
+
+func Union(sets ...StringSet) StringSet {
+	t := make(StringSet)
+	for _, s := range sets {
+		t = t.Union(s)
+	}
+	return t
+}
+
+func Intersect(sets ...StringSet) StringSet {
+	t := Union(sets...)
+	for _, s := range sets {
+		t = t.Intersect(s)
+	}
+	return t
+}

2021/aoc/stringset/stringset_test.go

@@ -0,0 +1,40 @@
+package stringset_test
+
+import (
+	"testing"
+
+	"github.com/jdkaplan/advent-of-code/aoc/stringset"
+)
+
+func TestMinus(t *testing.T) {
+	a := stringset.Runes("dab")
+	b := stringset.Runes("ab")
+	u := a.Minus(b)
+	if n := len(u); n != 1 {
+		t.Fatalf("Expected one value, got %d", n)
+	}
+	if v := u.Only(); v != "d" {
+		t.Errorf(`Expected value to be "d", got %s`, v)
+	}
+}
+
+func TestIntersect(t *testing.T) {
+	t.Run("pairwise", func(t *testing.T) {
+		u := stringset.Runes("dab").Intersect(stringset.Runes("ab"))
+		expected := stringset.Runes("ab")
+		if !u.Equal(expected) {
+			t.Errorf(`Expected value to be %s, got %s`, expected, u)
+		}
+	})
+
+	t.Run("multiple", func(t *testing.T) {
+		u := stringset.Intersect(
+			stringset.Runes("dab"),
+			stringset.Runes("ab"),
+		)
+		expected := stringset.Runes("ab")
+		if !u.Equal(expected) {
+			t.Errorf(`Expected value to be %s, got %s`, expected, u)
+		}
+	})
+}