Solve day 5

day5/example.txt

@@ -0,0 +1,11 @@
+3-5
+10-14
+16-20
+12-18
+
+1
+5
+8
+11
+17
+32

day5/main.go

@@ -0,0 +1,123 @@
+package main
+
+import (
+	"bufio"
+	"cmp"
+	"fmt"
+	"io"
+	"log"
+	"os"
+	"slices"
+	"strconv"
+	"strings"
+)
+
+func main() {
+	f := os.Stdin
+	if len(os.Args) > 1 && os.Args[1] != "-" {
+		var err error
+		f, err = os.Open(os.Args[1])
+		if err != nil {
+			log.Fatal(err)
+		}
+		defer f.Close()
+	}
+
+	fresh, available, err := readIngredients(f)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	var availableFresh int
+	for _, id := range available {
+		for _, r := range fresh {
+			if r.Includes(id) {
+				availableFresh++
+				break
+			}
+		}
+	}
+
+	var freshIds int
+	compactFresh := compactedRanges(fresh)
+	for _, r := range compactFresh {
+		freshIds += r.to - r.from + 1
+	}
+
+	fmt.Println("available fresh:", availableFresh)
+	fmt.Println("total fresh:", freshIds)
+}
+
+type idsRange struct {
+	from, to int
+}
+
+func (r idsRange) Includes(n int) bool {
+	return r.from <= n && n <= r.to
+}
+
+func readIngredients(r io.Reader) (fresh []idsRange, available []int, err error) {
+	seenEmptyLine := false
+	sc := bufio.NewScanner(r)
+	for sc.Scan() {
+		if sc.Text() == "" {
+			seenEmptyLine = true
+			continue
+		}
+		if seenEmptyLine {
+			id, err := strconv.ParseUint(sc.Text(), 10, 0)
+			if err != nil {
+				return nil, nil, err
+			}
+			available = append(available, int(id))
+		} else {
+			r, err := parseRange(sc.Text())
+			if err != nil {
+				return nil, nil, err
+			}
+			fresh = append(fresh, r)
+		}
+	}
+	return fresh, available, nil
+}
+
+func parseRange(s string) (idsRange, error) {
+	before, after, ok := strings.Cut(s, "-")
+	if !ok {
+		return idsRange{}, fmt.Errorf("range %q: missing hyphen", s)
+	}
+	from, err := strconv.ParseUint(before, 10, 0)
+	if err != nil {
+		return idsRange{}, fmt.Errorf("range from: %w", err)
+	}
+	to, err := strconv.ParseUint(after, 10, 0)
+	if err != nil {
+		return idsRange{}, fmt.Errorf("range to: %w", err)
+	}
+	return idsRange{
+		from: int(from),
+		to:   int(to),
+	}, nil
+}
+
+func compactedRanges(ranges []idsRange) []idsRange {
+	ranges = slices.Clone(ranges)
+
+	slices.SortFunc(ranges, func(a, b idsRange) int {
+		if x := cmp.Compare(a.from, b.from); x != 0 {
+			return x
+		}
+		return cmp.Compare(a.to, b.to)
+	})
+
+	i := 0
+	for j := 1; j < len(ranges); j++ {
+		if !ranges[i].Includes(ranges[j].from) {
+			i++
+			ranges[i] = ranges[j]
+			continue
+		}
+		ranges[i].to = max(ranges[i].to, ranges[j].to)
+	}
+	return ranges[:i+1]
+}

day5/main_test.go

@@ -0,0 +1,68 @@
+package main
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func Test_compactedRanges(t *testing.T) {
+	tests := []struct {
+		name   string // description of this test case
+		ranges []idsRange
+		want   []idsRange
+	}{
+		{
+			name: "single",
+			ranges: []idsRange{
+				{0, 10},
+			},
+			want: []idsRange{
+				{0, 10},
+			},
+		},
+		{
+			name: "identical",
+			ranges: []idsRange{
+				{0, 10},
+				{0, 10},
+				{0, 10},
+				{20, 30},
+				{20, 30},
+			},
+			want: []idsRange{
+				{0, 10},
+				{20, 30},
+			},
+		},
+		{
+			name: "simple",
+			ranges: []idsRange{
+				{0, 10},
+				{2, 11},
+				{20, 30},
+			},
+			want: []idsRange{
+				{0, 11},
+				{20, 30},
+			},
+		},
+		{
+			name: "swallows",
+			ranges: []idsRange{
+				{0, 10},
+				{2, 8},
+				{20, 30},
+			},
+			want: []idsRange{
+				{0, 10},
+				{20, 30},
+			},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			assert.Equal(t, tt.want, compactedRanges(tt.ranges))
+		})
+	}
+}