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

package two

import (
	"bytes"
	"slices"
)

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) == 'A' {
				if func() bool {
					for _, n := range neighbours(current) {
						if graph.isOutOfBounds(n) {
							return true
						}

						if !slices.Contains([]rune{'M', 'S'}, graph.valueAt(n)) {
							return true
						}
					}
					return false
				}() {
					continue
				}

				ns := neighbours(current)
				matrix := newMatrix(
					graph.valueAt(current),
					graph.valueAt(ns[NW]),
					graph.valueAt(ns[NE]),
					graph.valueAt(ns[SE]),
					graph.valueAt(ns[SW]),
				)

				if matrix.isValid() {
					sum++
				}
			}
		}
	}

	return sum, nil
}