copy image from cachedImages

day-14/two.go

@@ -12,26 +12,28 @@ func cycleOnce(image img) {
 }
 
 // cycleMany cycles a single image for a given number of iterations
-// it also caches the index of the iteration for each image
+// it caches seen images as well as their location in the period
+// finally it copies the cached image with idx matching the interval to image.raw
 func cycleMany(image img, iterations int) {
-	cache := make(map[string]int)
+	cachedIndexes := make(map[string]int)
+	cachedImages := make(map[int][]string)
 	i, start := 0, 0
 	for ; i < iterations; i++ {
 		cycleOnce(image)
 
-		if idx, ok := cache[image.String()]; ok { // we found first repeated image
+		if idx, ok := cachedIndexes[image.String()]; ok { // we found first repeated image
 			start = idx
 			i++
 			break
 		}
 
-		cache[image.String()] = i + 1
+		cachedIndexes[image.String()] = i + 1
+		cachedImages[i+1] = make([]string, len(image.raw))
+		copy(cachedImages[i+1], image.raw)
 	}
+
 	period := i - start                                            // length of a full period
-	remaining := (iterations - i - 1) % period // number of cycles left in current period
+	copy(image.raw, cachedImages[start+((iterations-i-1)%period)]) // copy cachedImage into image.raw
-	for j := 0; j < remaining; j++ {
-		cycleOnce(image) // rotate to the final image in the period
-	}
 }
 
 // two returns the load of all boulders after 1000000000 cycles