Part 1 and first pass at Part 2

README.md

@@ -153,3 +153,13 @@ The solution for "fourteen" is:
 The result of subtracting the least from most common element quantities is 2988
 The result of subtracting the least from most common element quantities is 3572761917024
 ```
+
+### Day fifteen
+
+```sh
+$ ./aoc2021 --fifteen
+The solution for "fifteen" is:
+fifteen part 1 answer for path
+fifteen part 2 answer for path
+```
+

fifteen/input.txt

@@ -0,0 +1,100 @@
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fifteen/main.go

@@ -0,0 +1,25 @@
+package fifteen
+
+import "fmt"
+
+type Fifteen struct {
+	path path
+}
+
+func Init(filepath string) *Fifteen {
+	fifteen := &Fifteen{
+		path: path{},
+	}
+
+	fifteen.path.load(filepath)
+	return fifteen
+}
+
+func (d *Fifteen) Answer() string {
+	return fmt.Sprintf("The total risk of the least risky path is %d", d.path.totalRisk())
+}
+
+func (d *Fifteen) FollowUp() string {
+	scaled := d.path.scale(5, 5)
+	return fmt.Sprintf("The total risk of the least risky path is %d", scaled.totalRisk())
+}

fifteen/path.go

@@ -0,0 +1,215 @@
+package fifteen
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"strconv"
+	"strings"
+)
+
+type path struct {
+	riskLevel [][]int
+	width     int
+	height    int
+}
+
+type point struct {
+	x int
+	y int
+}
+
+func (p *path) load(filename string) error {
+	file, err := os.Open(filename)
+	if err != nil {
+		return err
+	}
+	defer file.Close()
+	scanner := bufio.NewScanner(file)
+
+	p.riskLevel = [][]int{}
+	for scanner.Scan() {
+		row := []int{}
+		for _, n := range strings.Split(scanner.Text(), "") {
+			v, err := strconv.Atoi(string(n))
+			if err != nil {
+				return err
+			}
+
+			row = append(row, v)
+		}
+		p.riskLevel = append(p.riskLevel, row)
+	}
+
+	p.height = len(p.riskLevel)
+	p.width = len(p.riskLevel[0])
+
+	return nil
+}
+
+func (p *path) scale(sizeX int, sizeY int) *path {
+	scaledPath := &path{
+		width:  p.width * sizeX,
+		height: p.height * sizeY,
+	}
+
+	scaledPath.riskLevel = make([][]int, scaledPath.height)
+	for i := 0; i < scaledPath.height; i++ {
+		scaledPath.riskLevel[i] = make([]int, scaledPath.width)
+	}
+
+	for i := 0; i < sizeX; i++ {
+		for j := 0; j < sizeY; j++ {
+			for y := 0; y < p.height; y++ {
+				for x := 0; x < p.width; x++ {
+					risk := p.riskLevel[y][x] + i + j
+					for risk > 9 {
+						risk -= 9
+					}
+
+					scaledPath.riskLevel[(j*p.height)+y][(i*p.width)+x] = risk
+				}
+			}
+		}
+	}
+
+	return scaledPath
+}
+
+func (p *path) print() {
+	for y := 0; y < p.height; y++ {
+		row := ""
+		for x := 0; x < p.width; x++ {
+			row += fmt.Sprintf("%d", p.riskLevel[y][x])
+		}
+		fmt.Println(row)
+	}
+}
+
+func (p *path) totalRisk() int {
+	start := point{
+		x: 0,
+		y: 0,
+	}
+	end := point{
+		x: p.width - 1,
+		y: p.height - 1,
+	}
+
+	path := p.path(start, end)
+	total := 0
+
+	for i, point := range path {
+		if i == 0 {
+			continue
+		}
+		total += p.riskLevel[point.y][point.x]
+	}
+
+	return total
+}
+
+func minValue(distance map[point]int, nodes []point) (point, []point) {
+	var min *point
+	remaining := []point{}
+
+	for i := range nodes {
+		if min == nil {
+			min = &nodes[i]
+			continue
+		}
+
+		if distance[nodes[i]] < distance[*min] {
+			remaining = append(remaining, *min)
+			min = &nodes[i]
+		} else {
+			remaining = append(remaining, nodes[i])
+		}
+	}
+
+	return *min, remaining
+}
+
+func contains(nodes []point, x int, y int) bool {
+	for _, n := range nodes {
+		if n.x == x && n.y == y {
+			return true
+		}
+	}
+	return false
+}
+
+func (p *path) path(start point, end point) []point {
+	dist := map[point]int{}
+	prev := map[point]point{}
+	nodes := []point{}
+
+	for y := 0; y < p.height; y++ {
+		for x := 0; x < p.width; x++ {
+			point := point{x: x, y: y}
+			// Virtually infinite for worst case
+			dist[point] = 10 * (p.width + p.height)
+			nodes = append(nodes, point)
+		}
+	}
+	dist[start] = 0
+
+	for len(nodes) > 0 {
+		current, newNodes := minValue(dist, nodes)
+
+		// Check neigbours
+		neighbours := []point{}
+		// left
+		if current.x > 0 && contains(newNodes, current.x-1, current.y) {
+			left := point{
+				x: current.x - 1,
+				y: current.y,
+			}
+			neighbours = append(neighbours, left)
+		}
+		// up
+		if current.y > 0 && contains(newNodes, current.x, current.y-1) {
+			up := point{
+				x: current.x,
+				y: current.y - 1,
+			}
+			neighbours = append(neighbours, up)
+		}
+		// right
+		if current.x < p.width-1 && contains(newNodes, current.x+1, current.y) {
+			right := point{
+				x: current.x + 1,
+				y: current.y,
+			}
+			neighbours = append(neighbours, right)
+		}
+		// down
+		if current.y < p.height-1 && contains(newNodes, current.x, current.y+1) {
+			down := point{
+				x: current.x,
+				y: current.y + 1,
+			}
+			neighbours = append(neighbours, down)
+		}
+
+		for _, n := range neighbours {
+			cost := dist[current] + p.riskLevel[n.y][n.x]
+			if cost < dist[n] {
+				dist[n] = cost
+				prev[n] = current
+			}
+		}
+
+		nodes = newNodes
+	}
+
+	path := []point{end}
+	index := end
+	for index != start {
+		prefix := []point{prev[index]}
+		path = append(prefix, path...)
+		index = prev[index]
+	}
+
+	return path
+}

fifteen/path_test.go

@@ -0,0 +1,44 @@
+package fifteen
+
+import "testing"
+
+func Test_read(t *testing.T) {
+	p := path{}
+	if err := p.load("test_input.txt"); err != nil {
+		t.Log(err)
+		t.FailNow()
+	}
+
+	if len(p.riskLevel) != 10 {
+		t.Logf("Expected 10 rows, found %d", len(p.riskLevel))
+		t.Fail()
+	}
+
+	if len(p.riskLevel[0]) != 10 {
+		t.Logf("Expected 10 rows, found %d", len(p.riskLevel[0]))
+		t.Fail()
+	}
+}
+
+func Test_totalRisk(t *testing.T) {
+	p := path{}
+	p.load("test_input.txt")
+
+	if value := p.totalRisk(); value != 40 {
+		t.Logf("Expected a total risk of 40, found %d", value)
+		t.Fail()
+	}
+}
+
+func Test_totalRiskScaled(t *testing.T) {
+	p := path{}
+	p.load("test_input.txt")
+	p = *p.scale(5, 5)
+
+	p.print()
+
+	if value := p.totalRisk(); value != 315 {
+		t.Logf("Expected a total risk of 315, found %d", value)
+		t.Fail()
+	}
+}

fifteen/test_input.txt

@@ -0,0 +1,10 @@
+1163751742
+1381373672
+2136511328
+3694931569
+7463417111
+1319128137
+1359912421
+3125421639
+1293138521
+2311944581

main.go

@@ -7,6 +7,7 @@ import (
 
 	"unsupervised.ca/aoc2021/eight"
 	"unsupervised.ca/aoc2021/eleven"
+	"unsupervised.ca/aoc2021/fifteen"
 	"unsupervised.ca/aoc2021/five"
 	"unsupervised.ca/aoc2021/four"
 	"unsupervised.ca/aoc2021/fourteen"
@@ -64,6 +65,8 @@ func main() {
 		day = thirteen.Init("thirteen/input.txt")
 	case "fourteen":
 		day = fourteen.Init("fourteen/input.txt")
+	case "fifteen":
+		day = fifteen.Init("fifteen/input.txt")
 	default:
 		fmt.Printf("%q does not have a solution.\n", flagParts[1])
 		help()