speed up p2...

day-16/two.go

@@ -1,5 +1,7 @@
 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{}
@@ -18,36 +20,47 @@ func spawn(i, j, direction int, lines []string) int {
 	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
 
-	var x = 0
-	for x < len(lines[0]) {
-		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
-		}
-		x++
+	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)
 	}
 
-	var y = 0
-	for y < len(lines) {
-		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
-		}
-		y++
+	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
+			}
+			y++
+		}(i)
 	}
 
+	wg.Wait()
+
 	return res
 }