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

package two

import (
	"bytes"
	"slices"
	"sync"
)

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) == '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
					}() {
						return
					}

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

					sumChan <- matrix.isValid()
				}
			}()
		}
	}

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

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

	return sum, nil
}