aoc2023/day-16/two.go

package main

import "sync"

// returns the number of unique nodes (reducing multiple nodes with different directions to one)
func uniqueNodes(move *mover) int {
	uniqueCoords := []coords{}
	for _, node := range move.nodes {
		if !coordInCoords(node.coords, uniqueCoords) {
			uniqueCoords = append(uniqueCoords, node.coords)
		}
	}
	return len(uniqueCoords)
}

// spawn invoked a single runner with a single mover
func spawn(i, j, direction int, lines []string) int {
	m := newMover(newNode(i, j, direction))
	runner(m, lines)
	return uniqueNodes(m)
}

var wg sync.WaitGroup

// two returns the highest energized value for any beam spawn point/direction
func two(lines []string) int {
	res := 0
	n := 0

	for i := 0; i < len(lines[0]); i++ {
		wg.Add(1)
		go func(x int) {
			defer wg.Done()

			n = spawn(x, 0, S, lines)
			if n > res {
				res = n
			}
			n = spawn(x, len(lines[0])-1, N, lines)
			if n > res {
				res = n
			}
		}(i)
	}

	for i := 0; i < len(lines); i++ {
		wg.Add(1)
		go func(y int) {
			defer wg.Done()

			n = spawn(0, y, E, lines)
			if n > res {
				res = n
			}
			n = spawn(len(lines[0])-1, y, W, lines)
			if n > res {
				res = n
			}
		}(i)
	}

	wg.Wait()

	return res
}