feat(puzzles): Implement solution for 2015/day03 (#87)

* feat(puzzles): Add spec; skeleton and tests for 2015/day03

* feat(puzzles): Register 2015/day03 solver

* feat(puzzles): Implement 2015/day03 part1

* tests: Update regression tests

* feat(puzzles): Add spec for 2015/day03 part2

* feat(puzzles): Add tests for 2015/day03 part2

* feat(puzzles): Implement 2015/day03 part2

* style: Fix fmt

* refactor(puzzles): Refactor 2015/day03

* tests: Update regression tests

Author: obalunenko

internal/puzzles/solutions/2015/day03/solution.go

@@ -0,0 +1,199 @@
+// Package day03 contains solution for https://adventofcode.com/2015/day/3 puzzle.
+package day03
+
+import (
+	"bufio"
+	"errors"
+	"fmt"
+	"io"
+	"strconv"
+
+	"github.com/obalunenko/advent-of-code/internal/puzzles"
+)
+
+func init() {
+	puzzles.Register(solution{})
+}
+
+type solution struct{}
+
+func (solution) Day() string {
+	return puzzles.Day03.String()
+}
+
+func (solution) Year() string {
+	return puzzles.Year2015.String()
+}
+
+func (solution) Part1(input io.Reader) (string, error) {
+	const santaNum = 1
+
+	return solve(input, santaNum)
+}
+
+func (solution) Part2(input io.Reader) (string, error) {
+	const santaNum = 2
+
+	return solve(input, santaNum)
+}
+
+func solve(input io.Reader, santaNum int) (string, error) {
+	addresses, err := makeAddressesList(input)
+	if err != nil {
+		return "", fmt.Errorf("make addresses: %w", err)
+	}
+
+	deliverymen := make([]deliveryman, 0, santaNum)
+
+	for i := 0; i < santaNum; i++ {
+		deliverymen = append(deliverymen, newSanta())
+	}
+
+	delivery := newSantaDelivery(deliverymen)
+
+	if err = delivery.deliver(addresses); err != nil {
+		return "", fmt.Errorf("deliver: %w", err)
+	}
+
+	visited := delivery.housesVisited()
+
+	return strconv.Itoa(visited), nil
+}
+
+func makeAddressesList(input io.Reader) ([]string, error) {
+	reader := bufio.NewReader(input)
+
+	var list []string
+
+	for {
+		r, _, err := reader.ReadRune()
+		if err != nil {
+			if errors.Is(err, io.EOF) {
+				break
+			}
+
+			return nil, fmt.Errorf("read rune: %w", err)
+		}
+
+		if r == '\n' {
+			continue
+		}
+
+		list = append(list, string(r))
+	}
+
+	return list, nil
+}
+
+type grid struct {
+	x, y int
+}
+
+func newGrid() grid {
+	return grid{
+		x: 0,
+		y: 0,
+	}
+}
+
+var errUnknownDirection = errors.New("unknown direction")
+
+func (g *grid) move(m string) error {
+	const (
+		north = "^"
+		south = "v"
+		east  = ">"
+		west  = "<"
+	)
+
+	switch m {
+	case north:
+		g.y++
+	case south:
+		g.y--
+	case west:
+		g.x--
+	case east:
+		g.x++
+	default:
+		return errUnknownDirection
+	}
+
+	return nil
+}
+
+type santaDelivery struct {
+	santas []deliveryman
+}
+
+func newSantaDelivery(deliverymen []deliveryman) santaDelivery {
+	return santaDelivery{
+		santas: deliverymen,
+	}
+}
+
+func (s *santaDelivery) deliver(addresses []string) error {
+	for i, address := range addresses {
+		snt := s.santas[0]
+
+		if i%2 == 0 && len(s.santas) == 2 {
+			snt = s.santas[1]
+		}
+
+		if err := snt.visit(address); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+func (s *santaDelivery) housesVisited() int {
+	total := make(map[grid]int)
+
+	for i := range s.santas {
+		snt := s.santas[i]
+
+		for address, count := range snt.housesVisited() {
+			total[address] += count
+		}
+	}
+
+	return len(total)
+}
+
+type deliveryman interface {
+	visit(address string) error
+	housesVisited() map[grid]int
+}
+
+type santa struct {
+	location grid
+	visited  map[grid]int
+}
+
+func newSanta() *santa {
+	startLoc := newGrid()
+
+	visited := make(map[grid]int)
+	visited[startLoc]++
+
+	return &santa{
+		location: startLoc,
+		visited:  visited,
+	}
+}
+
+func (s *santa) visit(address string) error {
+	if err := s.location.move(address); err != nil {
+		return fmt.Errorf("failed to visit address: %w", err)
+	}
+
+	s.visited[s.location]++
+
+	return nil
+}
+
+func (s santa) housesVisited() map[grid]int {
+	return s.visited
+}

internal/puzzles/solutions/2015/day03/solution_test.go

@@ -0,0 +1,153 @@
+package day03
+
+import (
+	"errors"
+	"io"
+	"strings"
+	"testing"
+	"testing/iotest"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func Test_solution_Year(t *testing.T) {
+	var s solution
+
+	want := "2015"
+	got := s.Year()
+
+	assert.Equal(t, want, got)
+}
+
+func Test_solution_Day(t *testing.T) {
+	var s solution
+
+	want := "3"
+	got := s.Day()
+
+	assert.Equal(t, want, got)
+}
+
+func Test_solution_Part1(t *testing.T) {
+	var s solution
+
+	type args struct {
+		input io.Reader
+	}
+
+	tests := []struct {
+		name    string
+		args    args
+		want    string
+		wantErr bool
+	}{
+		{
+			name: "> delivers presents to 2 houses: one at the starting location, and one to the east.",
+			args: args{
+				input: strings.NewReader(">\n"),
+			},
+			want:    "2",
+			wantErr: false,
+		},
+		{
+			name: "^>v< delivers presents to 4 houses in a square, including twice to the house at his starting/ending location.",
+			args: args{
+				input: strings.NewReader("^>v<\n"),
+			},
+			want:    "4",
+			wantErr: false,
+		},
+		{
+			name: "^v^v^v^v^v delivers a bunch of presents to some very lucky children at only 2 houses.",
+			args: args{
+				input: strings.NewReader("^v^v^v^v^v\n"),
+			},
+			want:    "2",
+			wantErr: false,
+		},
+		{
+			name: "",
+			args: args{
+				input: iotest.ErrReader(errors.New("custom error")),
+			},
+			want:    "",
+			wantErr: true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := s.Part1(tt.args.input)
+			if tt.wantErr {
+				assert.Error(t, err)
+
+				return
+			}
+
+			assert.NoError(t, err)
+			assert.Equal(t, tt.want, got)
+		})
+	}
+}
+
+func Test_solution_Part2(t *testing.T) {
+	var s solution
+
+	type args struct {
+		input io.Reader
+	}
+
+	tests := []struct {
+		name    string
+		args    args
+		want    string
+		wantErr bool
+	}{
+		{
+			name: "^v delivers presents to 3 houses, because Santa goes north, and then Robo-Santa goes south.",
+			args: args{
+				input: strings.NewReader("^v\n"),
+			},
+			want:    "3",
+			wantErr: false,
+		},
+		{
+			name: "^>v< now delivers presents to 3 houses, and Santa and Robo-Santa end up back where they started.",
+			args: args{
+				input: strings.NewReader("^>v<\n"),
+			},
+			want:    "3",
+			wantErr: false,
+		},
+		{
+			name: "^v^v^v^v^v now delivers presents to 11 houses, with Santa going one direction and Robo-Santa going the other.",
+			args: args{
+				input: strings.NewReader("^v^v^v^v^v\n"),
+			},
+			want:    "11",
+			wantErr: false,
+		},
+		{
+			name: "",
+			args: args{
+				input: iotest.ErrReader(errors.New("custom error")),
+			},
+			want:    "",
+			wantErr: true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := s.Part2(tt.args.input)
+			if tt.wantErr {
+				assert.Error(t, err)
+
+				return
+			}
+
+			assert.NoError(t, err)
+			assert.Equal(t, tt.want, got)
+		})
+	}
+}

internal/puzzles/solutions/2015/day03/spec.md

@@ -0,0 +1,35 @@
+# --- Day 3: Perfectly Spherical Houses in a Vacuum ---
+
+## --- Part One ---
+
+Santa is delivering presents to an infinite two-dimensional grid of houses.
+
+He begins by delivering a present to the house at his starting location, and then an elf at the North Pole calls 
+him via radio and tells him where to move next. Moves are always exactly one house to the north (`^`), south (`v`), 
+east (`>`), or west (`<`). After each move, he delivers another present to the house at his new location.
+
+However, the elf back at the North Pole has had a little too much eggnog, and so his directions are a little off, 
+and Santa ends up visiting some houses more than once. How many houses receive at least one present?
+
+### For example:
+
+- `>` delivers presents to `2` houses: one at the starting location, and one to the east.
+- `^>v<` delivers presents to `4` houses in a square, including twice to the house at his starting/ending location.
+- `^v^v^v^v^v` delivers a bunch of presents to some very lucky children at only 2 houses.
+
+## --- Part Two ---
+
+The next year, to speed up the process, Santa creates a robot version of himself, Robo-Santa, to deliver presents with 
+him.
+
+Santa and Robo-Santa start at the same location (delivering two presents to the same starting house), 
+then take turns moving based on instructions from the elf, who is eggnoggedly reading from the same script as the 
+previous year.
+
+This year, how many houses receive at least one present?
+
+### For example:
+
+- `^v` delivers presents to `3` houses, because Santa goes north, and then Robo-Santa goes south.
+- `^>v<` now delivers presents to `3` houses, and Santa and Robo-Santa end up back where they started.
+- `^v^v^v^v^v` now delivers presents to `11` houses, with Santa going one direction and Robo-Santa going the other.

internal/puzzles/solutions/register_2015.go

@@ -8,4 +8,6 @@ import (
 	_ "github.com/obalunenko/advent-of-code/internal/puzzles/solutions/2015/day01"
 	// register day02 solution.
 	_ "github.com/obalunenko/advent-of-code/internal/puzzles/solutions/2015/day02"
+	// register day03 solution.
+	_ "github.com/obalunenko/advent-of-code/internal/puzzles/solutions/2015/day03"
 )