Add solution for Day 8

Signed-off-by: Knut Ahlers <knut@ahlers.me>

day08.go

@@ -0,0 +1,146 @@
+package aoc2019
+
+import (
+	"image"
+	"image/color"
+	"image/png"
+	"io/ioutil"
+	"math"
+	"os"
+	"strconv"
+	"strings"
+
+	"github.com/pkg/errors"
+)
+
+const (
+	day08ColorBlack int = iota
+	day08ColorWhite
+	day08ColorTransparent
+)
+
+type day08Layer struct {
+	data []int
+	w, h int
+}
+
+func (d day08Layer) countNumber(n int) int {
+	var count int
+
+	for _, v := range d.data {
+		if v == n {
+			count++
+		}
+	}
+
+	return count
+}
+
+func day08ComposeLayers(layers []day08Layer) day08Layer {
+	var finalLayerData = make([]int, layers[0].w*layers[0].h)
+
+	for i := len(layers) - 1; i >= 0; i-- {
+		for idx, col := range layers[i].data {
+			if col == day08ColorTransparent {
+				// Transparent, ignore
+				continue
+			}
+
+			finalLayerData[idx] = col
+		}
+	}
+
+	return day08Layer{data: finalLayerData, w: layers[0].w, h: layers[0].h}
+}
+
+func day08ParseToLayers(in string, w, h int) ([]day08Layer, error) {
+	var layers []day08Layer
+
+	if len(in)%(w*h) != 0 {
+		return nil, errors.Errorf("Unexpected input length for format %dx%d: %d", w, h, len(in))
+	}
+
+	var pos int
+	for pos < len(in) {
+		var lData []int
+		for _, c := range in[pos : pos+w*h] {
+			v, err := strconv.Atoi(string(c))
+			if err != nil {
+				return nil, errors.Wrap(err, "Unable to parse digit")
+			}
+			lData = append(lData, v)
+		}
+
+		layers = append(layers, day08Layer{data: lData, w: w, h: h})
+		pos += w * h
+	}
+
+	return layers, nil
+}
+
+func day08RenderLayer(layer day08Layer) image.Image {
+	img := image.NewRGBA(image.Rect(0, 0, layer.w, layer.h))
+
+	for idx, px := range layer.data {
+		var (
+			x = idx % layer.w
+			y = idx / layer.w
+		)
+
+		switch px {
+		case day08ColorBlack:
+			img.SetRGBA(x, y, color.RGBA{0x0, 0x0, 0x0, 0xff})
+		case day08ColorWhite:
+			img.SetRGBA(x, y, color.RGBA{0xff, 0xff, 0xff, 0xff})
+		}
+	}
+
+	return img
+}
+
+func solveDay8Part1(inFile string) (int, error) {
+	raw, err := ioutil.ReadFile(inFile)
+	if err != nil {
+		return 0, errors.Wrap(err, "Unable to read input file")
+	}
+
+	layers, err := day08ParseToLayers(strings.TrimSpace(string(raw)), 25, 6)
+	if err != nil {
+		return 0, errors.Wrap(err, "Unable to parse layers")
+	}
+
+	var (
+		fewest = math.MaxInt64
+		layer  day08Layer
+	)
+	for _, l := range layers {
+		if n := l.countNumber(0); n < fewest {
+			fewest = n
+			layer = l
+		}
+	}
+
+	return layer.countNumber(1) * layer.countNumber(2), nil
+}
+
+func solveDay8Part2(inFile string) error {
+	raw, err := ioutil.ReadFile(inFile)
+	if err != nil {
+		return errors.Wrap(err, "Unable to read input file")
+	}
+
+	layers, err := day08ParseToLayers(strings.TrimSpace(string(raw)), 25, 6)
+	if err != nil {
+		return errors.Wrap(err, "Unable to parse layers")
+	}
+
+	img := day08RenderLayer(day08ComposeLayers(layers))
+
+	f, err := os.Create("day08_image.png")
+	if err != nil {
+		return errors.Wrap(err, "Unable to open result file")
+	}
+	defer f.Close()
+
+	return errors.Wrap(png.Encode(f, img), "Unable to render image")
+}

day08_test.go

@@ -0,0 +1,59 @@
+package aoc2019
+
+import (
+	"reflect"
+	"testing"
+)
+
+func TestDay08ComposeLayers(t *testing.T) {
+	var (
+		exp = []int{0, 1, 1, 0}
+		in  = "0222112222120000"
+		w   = 2
+		h   = 2
+	)
+
+	layers, err := day08ParseToLayers(in, w, h)
+	if err != nil {
+		t.Fatalf("Layer parser failed: %s", err)
+	}
+
+	layer := day08ComposeLayers(layers)
+	if !reflect.DeepEqual(layer.data, exp) {
+		t.Errorf("Did not yield expected composed layer: exp=%+v got=%+v", exp, layer.data)
+	}
+}
+
+func TestDay08ParseToLayers(t *testing.T) {
+	var (
+		in = "123456789012"
+		w  = 3
+		h  = 2
+	)
+
+	layers, err := day08ParseToLayers(in, w, h)
+	if err != nil {
+		t.Fatalf("Layer parser failed: %s", err)
+	}
+
+	if len(layers) != 2 || !reflect.DeepEqual(layers[0].data, []int{1, 2, 3, 4, 5, 6}) || !reflect.DeepEqual(layers[1].data, []int{7, 8, 9, 0, 1, 2}) {
+		t.Errorf("Did not yield expected layers (123 456) (789 012): got=%#v", layers)
+	}
+}
+
+func TestCalculateDay8_Part1(t *testing.T) {
+	count, err := solveDay8Part1("day08_input.txt")
+	if err != nil {
+		t.Fatalf("Day 8 solver failed: %s", err)
+	}
+
+	t.Logf("Solution Day 8 Part 1: %d", count)
+}
+
+func TestCalculateDay8_Part2(t *testing.T) {
+	if err := solveDay8Part2("day08_input.txt"); err != nil {
+		t.Fatalf("Day 8 solver failed: %s", err)
+	}
+
+	t.Log("Solution Day 8 Part 2: See day08_image.png")
+}