Day 20: Part 1 and 2

Signed-off-by: James Griffin <james@unsupervised.ca>

main.go

@@ -3,7 +3,7 @@ package main
 import (
 	"fmt"
 
-	"github.com/thatguygriff/aoc2020/nineteen"
+	"github.com/thatguygriff/aoc2020/twenty"
 )
 
 func main() {
@@ -80,6 +80,10 @@ func main() {
 	// fmt.Println(eighteen.PartTwo())
 
 	// Day 19
-	fmt.Println(nineteen.PartOne())
-	fmt.Println(nineteen.PartTwo())
+	// fmt.Println(nineteen.PartOne())
+	// fmt.Println(nineteen.PartTwo())
+
+	// Day 20
+	fmt.Println(twenty.PartOne())
+	fmt.Println(twenty.PartTwo())
 }

twenty/day_twenty.go

@@ -0,0 +1,599 @@
+package twenty
+
+import (
+	"bufio"
+	"fmt"
+	"math"
+	"os"
+	"strings"
+)
+
+type tile struct {
+	id        int
+	something [][]bool
+
+	edges   []string
+	matches map[int]bool
+}
+
+type message struct {
+	tiles []tile
+	grid  [][]*tile
+
+	image [][]bool
+}
+
+func (t *tile) edge(side string) string {
+	border := ""
+	switch side {
+	case "top":
+		for _, c := range t.something[0] {
+			if c {
+				border += "#"
+			} else {
+				border += "."
+			}
+		}
+	case "bottom":
+		for _, c := range t.something[9] {
+			if c {
+				border += "#"
+			} else {
+				border += "."
+			}
+		}
+	case "left":
+		for _, row := range t.something {
+			if row[0] {
+				border += "#"
+			} else {
+				border += "."
+			}
+		}
+	case "right":
+		for _, row := range t.something {
+			if row[9] {
+				border += "#"
+			} else {
+				border += "."
+			}
+		}
+	}
+
+	return border
+}
+
+func (t *tile) flip() {
+	flipped := [][]bool{}
+	flipped = make([][]bool, 10)
+	for i := 0; i < 10; i++ {
+		flipped[i] = make([]bool, 10)
+	}
+
+	for y := 0; y < 10; y++ {
+		for x := 0; x < 10; x++ {
+			flipped[y][x] = t.something[9-y][9-x]
+		}
+	}
+
+	t.something = flipped
+}
+
+func (t *tile) flipY() {
+	flipped := [][]bool{}
+	flipped = make([][]bool, 10)
+	for i := 0; i < 10; i++ {
+		flipped[i] = make([]bool, 10)
+	}
+
+	for y := 0; y < 10; y++ {
+		for x := 0; x < 10; x++ {
+			flipped[y][x] = t.something[9-y][x]
+		}
+	}
+
+	t.something = flipped
+}
+
+func (t *tile) rotate() {
+	rotated := [][]bool{}
+	rotated = make([][]bool, 10)
+	for i := 0; i < 10; i++ {
+		rotated[i] = make([]bool, 10)
+	}
+
+	for y := 0; y < 10; y++ {
+		for x := 0; x < 10; x++ {
+			rotated[x][9-y] = t.something[y][x]
+		}
+	}
+
+	t.something = rotated
+}
+
+func (m *message) load(filename string) error {
+	file, err := os.Open(filename)
+	if err != nil {
+		return err
+	}
+	defer file.Close()
+
+	m.tiles = []tile{}
+
+	scanner := bufio.NewScanner(file)
+	var t *tile
+	for scanner.Scan() {
+		if strings.Contains(scanner.Text(), "Tile") {
+			t = &tile{}
+			count, err := fmt.Sscanf(scanner.Text(), "Tile %4d:", &t.id)
+
+			if count != 1 || err != nil {
+				return fmt.Errorf("Unable to parse %s", scanner.Text())
+			}
+			continue
+		}
+
+		if scanner.Text() == "" {
+			m.tiles = append(m.tiles, *t)
+			t = nil
+			continue
+		}
+
+		if t != nil {
+			row := []bool{}
+			for _, c := range scanner.Text() {
+				switch string(c) {
+				case ".":
+					row = append(row, false)
+				case "#":
+					row = append(row, true)
+				}
+			}
+
+			t.something = append(t.something, row)
+		}
+	}
+
+	if t != nil {
+		m.tiles = append(m.tiles, *t)
+	}
+
+	for i := 0; i < len(m.tiles); i++ {
+		m.tiles[i].matches = map[int]bool{}
+		m.tiles[i].edges = []string{}
+		m.tiles[i].edges = append(m.tiles[i].edges, m.tiles[i].edge("top"))
+		m.tiles[i].edges = append(m.tiles[i].edges, m.tiles[i].edge("bottom"))
+		m.tiles[i].edges = append(m.tiles[i].edges, m.tiles[i].edge("left"))
+		m.tiles[i].edges = append(m.tiles[i].edges, m.tiles[i].edge("right"))
+		m.tiles[i].flip()
+		m.tiles[i].edges = append(m.tiles[i].edges, m.tiles[i].edge("top"))
+		m.tiles[i].edges = append(m.tiles[i].edges, m.tiles[i].edge("bottom"))
+		m.tiles[i].edges = append(m.tiles[i].edges, m.tiles[i].edge("left"))
+		m.tiles[i].edges = append(m.tiles[i].edges, m.tiles[i].edge("right"))
+		m.tiles[i].flip()
+	}
+
+	gridSize := int(math.Sqrt(float64(len(m.tiles))))
+	m.grid = make([][]*tile, gridSize)
+	for i := 0; i < gridSize; i++ {
+		m.grid[i] = make([]*tile, gridSize)
+	}
+
+	m.image = make([][]bool, gridSize*8)
+	for i := 0; i < gridSize*8; i++ {
+		m.image[i] = make([]bool, gridSize*8)
+	}
+
+	return nil
+}
+
+func (m *message) findCorners() []tile {
+	// Compute neighbours
+	for i := 0; i < len(m.tiles); i++ {
+		for j := 0; j < len(m.tiles); j++ {
+			if i == j {
+				continue
+			}
+
+			for _, iEdge := range m.tiles[i].edges {
+				for _, jEdge := range m.tiles[j].edges {
+					if iEdge == jEdge {
+						m.tiles[i].matches[m.tiles[j].id] = true
+					}
+				}
+			}
+		}
+	}
+
+	corners := []tile{}
+	// Find neighbours with only 2 matches
+	for i := 0; i < len(m.tiles); i++ {
+		if len(m.tiles[i].matches) == 2 {
+			corners = append(corners, m.tiles[i])
+		}
+	}
+
+	return corners
+}
+
+func (m *message) getTile(id int) *tile {
+	for _, t := range m.tiles {
+		if t.id == id {
+			return &t
+		}
+	}
+	return nil
+}
+
+func (m *message) inGrid(id int) bool {
+	for y := 0; y < len(m.grid); y++ {
+		for x := 0; x < len(m.grid); x++ {
+			if m.grid[y][x] != nil {
+				if id == m.grid[y][x].id {
+					return true
+				}
+			}
+		}
+	}
+
+	return false
+}
+
+func (m *message) layout() bool {
+	corners := m.findCorners()
+	for i := range corners {
+		m.grid[0][0] = &corners[i]
+		if m.placeNeighbours(0, 0) {
+			return true
+		}
+
+		m.grid[0][0] = &corners[i]
+		m.grid[0][0].rotate()
+		if m.placeNeighbours(0, 0) {
+			return true
+		}
+
+		m.grid[0][0] = &corners[i]
+		m.grid[0][0].rotate()
+		if m.placeNeighbours(0, 0) {
+			return true
+		}
+
+		m.grid[0][0] = &corners[i]
+		m.grid[0][0].rotate()
+		if m.placeNeighbours(0, 0) {
+			return true
+		}
+
+		m.grid[0][0] = &corners[i]
+		m.grid[0][0].rotate()
+		m.grid[0][0].flip()
+		if m.placeNeighbours(0, 0) {
+			return true
+		}
+
+		m.grid[0][0] = &corners[i]
+		m.grid[0][0].rotate()
+		if m.placeNeighbours(0, 0) {
+			return true
+		}
+
+		m.grid[0][0] = &corners[i]
+		m.grid[0][0].rotate()
+		if m.placeNeighbours(0, 0) {
+			return true
+		}
+
+		m.grid[0][0] = &corners[i]
+		m.grid[0][0].rotate()
+		if m.placeNeighbours(0, 0) {
+			return true
+		}
+	}
+	return false
+}
+
+func (m *message) placeNeighbours(x, y int) bool {
+	allGood := true
+
+	if x+1 >= len(m.grid) && y+1 >= len(m.grid) {
+		return true
+	}
+
+	possibleTiles := []tile{}
+	for id := range m.grid[y][x].matches {
+		if !m.inGrid(id) {
+			possibleTiles = append(possibleTiles, *m.getTile(id))
+		}
+	}
+
+	if x+1 < len(m.grid) {
+		if m.grid[y][x+1] == nil {
+			right := m.grid[y][x].edge("right")
+			found := false
+			for _, p := range possibleTiles {
+				for _, match := range p.edges {
+					if match == right {
+						found = true
+						rfound := false
+						for i := 0; i < 4; i++ {
+							if right == p.edge("left") {
+								found = true
+								rfound = true
+								m.grid[y][x+1] = &p
+								allGood = m.placeNeighbours(x+1, y)
+								break
+							}
+
+							p.rotate()
+						}
+						if rfound {
+							break
+						}
+
+						p.flipY()
+						for i := 0; i < 4; i++ {
+							if right == p.edge("left") {
+								found = true
+								m.grid[y][x+1] = &p
+								allGood = m.placeNeighbours(x+1, y)
+								break
+							}
+
+							p.rotate()
+						}
+					}
+				}
+				if found {
+					break
+				}
+			}
+			allGood = found
+		} else {
+			allGood = m.grid[y][x].edge("right") == m.grid[y][x+1].edge("left")
+		}
+	}
+
+	if y+1 < len(m.grid) {
+		bottom := m.grid[y][x].edge("bottom")
+		found := false
+		for _, p := range possibleTiles {
+			for _, match := range p.edges {
+				if match == bottom {
+					found = true
+					rfound := false
+					for i := 0; i < 4; i++ {
+						if bottom == p.edge("top") {
+							found = true
+							rfound = true
+							m.grid[y+1][x] = &p
+							allGood = m.placeNeighbours(x, y+1)
+							break
+						}
+
+						p.rotate()
+					}
+					if rfound {
+						break
+					}
+
+					p.flipY()
+					for i := 0; i < 4; i++ {
+						if bottom == p.edge("top") {
+							found = true
+							m.grid[y+1][x] = &p
+							allGood = m.placeNeighbours(x, y+1)
+							break
+						}
+
+						p.rotate()
+					}
+				}
+			}
+			if found {
+				break
+			}
+
+			allGood = false
+		}
+	}
+
+	if !allGood {
+		m.grid[y][x] = nil
+	}
+
+	return allGood
+}
+
+func (m *message) combineTiles() bool {
+	for y := 0; y < len(m.grid); y++ {
+		for x := 0; x < len(m.grid); x++ {
+			if m.grid[y][x] == nil {
+				return false
+			}
+		}
+	}
+
+	for y := 0; y < len(m.grid); y++ {
+		for x := 0; x < len(m.grid); x++ {
+			for tY := 1; tY < len(m.grid[y][x].something)-1; tY++ {
+				for tX := 1; tX < len(m.grid[y][x].something[tY])-1; tX++ {
+					imageY := (y * (len(m.grid[y][x].something) - 2)) + (tY - 1)
+					imageX := (x * (len(m.grid[y][x].something[tY]) - 2)) + (tX - 1)
+					m.image[imageY][imageX] = m.grid[y][x].something[tY][tX]
+				}
+			}
+		}
+	}
+
+	return true
+}
+
+func (m *message) rotateImage() {
+	rotated := [][]bool{}
+	rotated = make([][]bool, len(m.image))
+	for i := 0; i < len(m.image); i++ {
+		rotated[i] = make([]bool, len(m.image))
+	}
+
+	for y := 0; y < 10; y++ {
+		for x := 0; x < 10; x++ {
+			rotated[x][9-y] = m.image[y][x]
+		}
+	}
+
+	m.image = rotated
+}
+
+func (m *message) flipImage() {
+	flipped := [][]bool{}
+	flipped = make([][]bool, len(m.image))
+	for i := 0; i < len(m.image); i++ {
+		flipped[i] = make([]bool, len(m.image))
+	}
+
+	for y := 0; y < 10; y++ {
+		for x := 0; x < 10; x++ {
+			flipped[y][x] = m.image[9-y][x]
+		}
+	}
+
+	m.image = flipped
+}
+
+func (m *message) printGrid() {
+	output := ""
+	for y := 0; y < len(m.grid); y++ {
+		for tY := 0; tY < 10; tY++ {
+			for x := 0; x < len(m.grid[y]); x++ {
+				for tX := 0; tX < 10; tX++ {
+					if m.grid[y][x].something[tY][tX] {
+						output += "#"
+					} else {
+						output += "."
+					}
+				}
+			}
+			output += "\n"
+		}
+	}
+
+	fmt.Printf(output)
+}
+
+func (m *message) printImage() {
+	output := ""
+	for _, row := range m.image {
+		for _, val := range row {
+			if val {
+				output += "#"
+			} else {
+				output += "."
+			}
+		}
+		output += "\n"
+	}
+
+	fmt.Printf(output)
+}
+
+func (m *message) alignMonsters() bool {
+	for i := 0; i < 4; i++ {
+		count := m.seaMonsters()
+		if count > 0 {
+			return true
+		}
+
+		m.rotateImage()
+	}
+	m.flipImage()
+	for i := 0; i < 4; i++ {
+		count := m.seaMonsters()
+		if count > 0 {
+			return true
+		}
+
+		m.rotateImage()
+	}
+	return false
+}
+
+func (m *message) cornerProduct() int {
+	corners := m.findCorners()
+	if len(corners) != 4 {
+		return -1
+	}
+
+	product := 1
+
+	for _, tile := range corners {
+		product *= tile.id
+	}
+
+	return product
+}
+
+func (m *message) seaMonsters() int {
+	monsters := 0
+	for y := 0; y < len(m.image)-2; y++ {
+		for x := 0; x < len(m.image[0])-19; x++ {
+			// Check if this is a valid seamonster
+			if m.image[y][x+18] &&
+				m.image[y+1][x] &&
+				m.image[y+1][x+5] &&
+				m.image[y+1][x+6] &&
+				m.image[y+1][x+11] &&
+				m.image[y+1][x+12] &&
+				m.image[y+1][x+17] &&
+				m.image[y+1][x+18] &&
+				m.image[y+1][x+19] &&
+				m.image[y+2][x+1] &&
+				m.image[y+2][x+4] &&
+				m.image[y+2][x+7] &&
+				m.image[y+2][x+10] &&
+				m.image[y+2][x+13] &&
+				m.image[y+2][x+16] {
+				monsters++
+			}
+		}
+	}
+	return monsters
+}
+
+func (m *message) countRoughness() int {
+	monsters := m.seaMonsters() * 15
+	total := 0
+	for y := 0; y < len(m.image); y++ {
+		for x := 0; x < len(m.image[0]); x++ {
+			if m.image[y][x] {
+				total++
+			}
+		}
+	}
+
+	return total - monsters
+}
+
+// PartOne Find the product of the ids of the four corners
+func PartOne() string {
+	m := message{}
+	if err := m.load("twenty/input.txt"); err != nil {
+		return err.Error()
+	}
+
+	return fmt.Sprintf("The product of the four corners is %d", m.cornerProduct())
+}
+
+// PartTwo How many # are not seamonsters.
+func PartTwo() string {
+	m := message{}
+	if err := m.load("twenty/input.txt"); err != nil {
+		return err.Error()
+	}
+
+	m.layout()
+	m.combineTiles()
+	m.alignMonsters()
+
+	return fmt.Sprintf("There are %d # that are not seamonsters", m.countRoughness())
+}

twenty/day_twenty_test.go

@@ -0,0 +1,75 @@
+package twenty
+
+import "testing"
+
+func Test_tile_load(t *testing.T) {
+	m := message{}
+	m.load("sample.txt")
+
+	if len(m.tiles) != 9 {
+		t.Logf("Expected 9 tiles to be loaded, got %d", len(m.tiles))
+		t.FailNow()
+	}
+
+	if len(m.grid) != 3 && len(m.grid[0]) != 3 {
+		t.Logf("Expected a 3x3 grid, got %dx%d", len(m.grid), len(m.grid[0]))
+		t.FailNow()
+	}
+}
+
+func Test_arrange_tile(t *testing.T) {
+	m := message{}
+	m.load("sample.txt")
+
+	result := m.cornerProduct()
+	if result != 20899048083289 {
+		t.Logf("Expected a result of 20899048083289, got %d", result)
+		t.FailNow()
+	}
+}
+
+func Test_arrange_input(t *testing.T) {
+	m := message{}
+	m.load("input.txt")
+
+	result := m.cornerProduct()
+	if result == -1 {
+		t.Logf("Expected a result other than -1, got %d", result)
+		t.FailNow()
+	}
+}
+
+func Test_count_monsters(t *testing.T) {
+	m := message{}
+	m.load("sample.txt")
+
+	grid := m.layout()
+	if !grid {
+		t.Log("Expected a grid")
+		t.FailNow()
+	}
+
+	m.combineTiles()
+	m.alignMonsters()
+
+	result := m.seaMonsters()
+	if result != 2 {
+		t.Logf("Expected 2 monsters, found %d", result)
+		t.FailNow()
+	}
+}
+
+func Test_count_roughness(t *testing.T) {
+	m := message{}
+	m.load("sample.txt")
+
+	m.layout()
+	m.combineTiles()
+	m.alignMonsters()
+
+	result := m.countRoughness()
+	if result != 273 {
+		t.Logf("Expected 273 # not part of a monster, found %d", result)
+		t.FailNow()
+	}
+}

twenty/monster.txt

@@ -0,0 +1,3 @@
+                  #
+#    ##    ##    ###
+ #  #  #  #  #  #

twenty/sample.txt

@@ -0,0 +1,107 @@
+Tile 2311:
+..##.#..#.
+##..#.....
+#...##..#.
+####.#...#
+##.##.###.
+##...#.###
+.#.#.#..##
+..#....#..
+###...#.#.
+..###..###
+
+Tile 1951:
+#.##...##.
+#.####...#
+.....#..##
+#...######
+.##.#....#
+.###.#####
+###.##.##.
+.###....#.
+..#.#..#.#
+#...##.#..
+
+Tile 1171:
+####...##.
+#..##.#..#
+##.#..#.#.
+.###.####.
+..###.####
+.##....##.
+.#...####.
+#.##.####.
+####..#...
+.....##...
+
+Tile 1427:
+###.##.#..
+.#..#.##..
+.#.##.#..#
+#.#.#.##.#
+....#...##
+...##..##.
+...#.#####
+.#.####.#.
+..#..###.#
+..##.#..#.
+
+Tile 1489:
+##.#.#....
+..##...#..
+.##..##...
+..#...#...
+#####...#.
+#..#.#.#.#
+...#.#.#..
+##.#...##.
+..##.##.##
+###.##.#..
+
+Tile 2473:
+#....####.
+#..#.##...
+#.##..#...
+######.#.#
+.#...#.#.#
+.#########
+.###.#..#.
+########.#
+##...##.#.
+..###.#.#.
+
+Tile 2971:
+..#.#....#
+#...###...
+#.#.###...
+##.##..#..
+.#####..##
+.#..####.#
+#..#.#..#.
+..####.###
+..#.#.###.
+...#.#.#.#
+
+Tile 2729:
+...#.#.#.#
+####.#....
+..#.#.....
+....#..#.#
+.##..##.#.
+.#.####...
+####.#.#..
+##.####...
+##..#.##..
+#.##...##.
+
+Tile 3079:
+#.#.#####.
+.#..######
+..#.......
+######....
+####.#..#.
+.#...#.##.
+#.#####.##
+..#.###...
+..#.......
+..#.###...