add day-20

day-20/internal/one/graph.go

@@ -0,0 +1,86 @@
+package one
+
+import (
+	"slices"
+	"strings"
+
+	"github.com/onyx-and-iris/aoc2024/day-20/internal/point"
+
+	"github.com/elliotchance/orderedmap/v3"
+)
+
+type graph struct {
+	start, end point.Point
+	data       []string
+}
+
+func newGraph(data []string) *graph {
+	return &graph{data: data}
+}
+
+func (g *graph) String() string {
+	return strings.Join(g.data, "\n")
+}
+
+func (g *graph) isOutOfBounds(p point.Point) bool {
+	return p.X < 1 || p.Y < 1 || p.Y >= len(g.data)-1 || p.X >= len(g.data[p.Y])-1
+}
+
+func (g *graph) valueAt(p point.Point) rune {
+	return rune(g.data[p.Y][p.X])
+}
+
+func (g *graph) isValidCheatPosition(p point.Point) bool {
+	allowed := []rune{'.', 'S', 'E'}
+
+	ns := neighbours(p)
+
+	return slices.Contains(allowed, g.valueAt(ns[N])) && slices.Contains(allowed, g.valueAt(ns[S])) ||
+		slices.Contains(allowed, g.valueAt(ns[W])) && slices.Contains(allowed, g.valueAt(ns[E]))
+}
+
+func (g *graph) getConnectingpoint(dir direction, p point.Point) point.Point {
+	ns := neighbours(p)
+
+	return ns[dir]
+}
+
+func (g *graph) set(p point.Point, value rune) {
+	g.data[p.Y] = replaceAtIndex(g.data[p.Y], value, p.X)
+}
+
+func (g *graph) path(
+	current point.Point,
+	om *orderedmap.OrderedMap[point.Point, int],
+	dist int,
+) *orderedmap.OrderedMap[point.Point, int] {
+	if current == g.end {
+		return om
+	}
+
+	var n point.Point
+	for _, n = range neighbours(current) {
+		_, ok := om.Get(n)
+		if ok {
+			continue
+		}
+
+		if g.valueAt(n) == '.' || g.valueAt(n) == 'E' {
+			break
+		}
+	}
+	om.Set(n, dist)
+
+	return g.path(n, om, dist+1)
+}
+
+func (g *graph) debug(path *orderedmap.OrderedMap[point.Point, int]) string {
+	temp := slices.Clone(g.data)
+	for n := range path.Keys() {
+		if g.valueAt(n) == cheatChar {
+			continue
+		}
+		temp[n.Y] = replaceAtIndex(temp[n.Y], 'O', n.X)
+	}
+	return strings.Join(temp, "\n")
+}

day-20/internal/one/neighbours.go

@@ -0,0 +1,21 @@
+package one
+
+import "github.com/onyx-and-iris/aoc2024/day-20/internal/point"
+
+type direction int
+
+const (
+	N direction = iota
+	E
+	S
+	W
+)
+
+func neighbours(p point.Point) [4]point.Point {
+	return [4]point.Point{
+		point.New(p.X, p.Y-1), // N
+		point.New(p.X+1, p.Y), // E
+		point.New(p.X, p.Y+1), // S
+		point.New(p.X-1, p.Y), // W
+	}
+}

day-20/internal/one/solve.go

@@ -0,0 +1,72 @@
+package one
+
+import (
+	"bytes"
+	"math"
+
+	"github.com/onyx-and-iris/aoc2024/day-20/internal/point"
+	log "github.com/sirupsen/logrus"
+
+	"github.com/elliotchance/orderedmap/v3"
+)
+
+const cheatChar = 'X'
+
+var Path *orderedmap.OrderedMap[point.Point, int]
+
+func Solve(buf []byte) (int, error) {
+	r := bytes.NewReader(buf)
+	graph, err := parseLines(r)
+	if err != nil {
+		return 0, err
+	}
+
+	Path = orderedmap.NewOrderedMap[point.Point, int]()
+	Path.Set(graph.start, 0)
+	Path = graph.path(graph.start, Path, 1)
+	log.Debugf("initial path: %d\n", Path.Len()-1)
+	log.Debugf("Unique path:\n%s\n", graph.debug(Path))
+
+	visited := make(map[point.Point]struct{})
+
+	var sum int
+	for point := range Path.Keys() {
+		for dir, n := range neighbours(point) {
+			if graph.isOutOfBounds(n) {
+				continue
+			}
+
+			if graph.valueAt(n) != '#' {
+				continue
+			}
+
+			if _, ok := visited[n]; ok {
+				continue
+			}
+
+			if graph.isValidCheatPosition(n) {
+				b := graph.getConnectingpoint(direction(dir), n)
+				graph.set(n, 'X')
+
+				v1, ok := Path.Get(point)
+				if !ok {
+					log.Fatalf("%v not in path", point)
+				}
+				v2, ok := Path.Get(b)
+				if !ok {
+					log.Fatalf("%v not in path", b)
+				}
+				diff := int(math.Abs(float64(v1-v2))) - 1
+
+				log.Debugf("diff: %d\n", diff)
+				if diff >= 100 {
+					sum++
+				}
+
+				visited[n] = struct{}{}
+			}
+		}
+	}
+
+	return sum, nil
+}

day-20/internal/one/solve_internal_test.go

@@ -0,0 +1,15 @@
+package one
+
+import (
+	_ "embed"
+	"os"
+	"testing"
+)
+
+//go:embed testdata/input.txt
+var data []byte
+
+func BenchmarkSolve(b *testing.B) {
+	os.Stdout, _ = os.Open(os.DevNull)
+	Solve(data)
+}

day-20/internal/one/util.go

@@ -0,0 +1,44 @@
+package one
+
+import (
+	"bufio"
+	"io"
+	"strings"
+
+	"github.com/onyx-and-iris/aoc2024/day-20/internal/point"
+)
+
+func parseLines(r io.Reader) (*graph, error) {
+	graph := newGraph(make([]string, 0))
+
+	var linecount int
+	scanner := bufio.NewScanner(r)
+	for scanner.Scan() {
+		line := scanner.Text()
+
+		if strings.Contains(line, "S") {
+			indx := strings.Index(line, "S")
+			graph.start = point.New(indx, linecount)
+		}
+		if strings.Contains(line, "E") {
+			indx := strings.Index(line, "E")
+			graph.end = point.New(indx, linecount)
+		}
+
+		graph.data = append(graph.data, line)
+
+		linecount++
+	}
+
+	if err := scanner.Err(); err != nil {
+		return nil, err
+	}
+
+	return graph, nil
+}
+
+func replaceAtIndex(s string, r rune, i int) string {
+	out := []rune(s)
+	out[i] = r
+	return string(out)
+}