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

package one

import (
	"bytes"
	"sync"

	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
	}

	wg := sync.WaitGroup{}
	sumChan := make(chan bool)

	for y := range graph.data {
		for x := range graph.data[y] {
			wg.Add(1)
			go func() {
				defer wg.Done()

				current := newPoint(x, y)
				if graph.valueAt(current) == 'X' {
					for _, n := range neighbours(current) {
						sumChan <- checkNeighbours(n, "MAS", graph)
					}
				}
			}()
		}
	}

	go func() {
		wg.Wait()
		close(sumChan)
	}()

	var sum int
	for val := range sumChan {
		if val {
			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)
}