aoc2024/day-20/internal/one/solve.go

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
}