aoc2024/day-04/internal/one/solve.go

package one

import (
	"bytes"

	log "github.com/sirupsen/logrus"
)

func Solve(buf []byte) (int, error) {
	r := bytes.NewReader(buf)
	graph, err := readLines(r)
	if err != nil {
		return 0, err
	}

	var sum int
	for y := range graph.data {
		for x := range graph.data[y] {
			current := newPoint(x, y)
			if graph.valueAt(current) == 'X' {
				for _, n := range neighbours(current) {
					if checkNeighbours(n, "MAS", graph) {
						sum++
					}
				}
			}
		}
	}

	return sum, nil
}

func checkNeighbours(n point, word string, g *graph) bool {
	if len(word) == 0 {
		log.Debug("we found a full XMAS")
		return true
	}

	if g.isOutOfBounds(n) {
		return false
	}

	if g.valueAt(n) != rune(word[0]) {
		return false
	}

	return checkNeighbours(neighbours(n)[n.direction], word[1:], g)
}