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

package one

import (
	"bytes"

	"github.com/onyx-and-iris/aoc2024/day-04/internal/util"

	log "github.com/sirupsen/logrus"
)

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

	var sum int

	for i := 0; i < len(lines); i++ {
		for j := 0; j < len(lines[i]); j++ {
			neighbours := newNeighbours(j, i)
			for _, n := range neighbours.all() {
				if n.x < 0 || n.y < 0 || n.y >= len(lines) || n.x >= len(lines[i]) {
					continue
				}

				if lines[i][j] == 'X' {
					if checkNeighbours(n, "MAS", lines) {
						sum++
					}
				}
			}
		}
	}

	return sum, nil
}

func checkNeighbours(n neighbour, word string, lines []string) bool {
	if len(word) == 0 {
		log.Debug("we found a full XMAS")
		return true
	}

	if n.x < 0 || n.y < 0 || n.y >= len(lines) || n.x >= len(lines[n.y]) {
		return false
	}

	if lines[n.y][n.x] != word[0] {
		return false
	}

	return checkNeighbours(newNeighbour(n.direction, n.x, n.y), word[1:], lines)
}