Slightly smarter day 11 solution

2024/day11/day11.go

@@ -8,47 +8,78 @@ import (
 	"strings"
 )
 
-func update(stones map[int]int) map[int]int {
-	processed := make(map[int]int)
-	for stone, count := range stones {
-		if stone == 0 {
-			processed[1] += count
-			continue
-		}
-
-		places := int(math.Log10(float64(stone))) + 1
-		if places%2 == 0 {
-			half := places / 2
-			divisor := int(math.Pow10(half))
-
-			left := stone / divisor
-			right := stone % divisor
-
-			processed[left] += count
-			processed[right] += count
-			continue
-		}
-
-		processed[stone*2024] += count
-	}
-
-	return processed
+type Key struct {
+	times, stone int
 }
 
-func Part1(stones map[int]int, steps int) int {
-	for i := 0; i < steps; i++ {
-		stones = update(stones)
+var splitCache = make(map[int][]int)
+var splitCacheHits, splitCacheMisses int
+
+var cache = make(map[Key]int)
+var cacheHits, cacheMisses int
+
+func split(stone int) (int, int) {
+	if val, ok := splitCache[stone]; ok {
+		splitCacheHits++
+		return val[0], val[1]
 	}
 
-	sum := 0
-	for _, count := range stones {
-		sum += count
-	}
+	splitCacheMisses++
 
-	return sum
+	half := (int(math.Log10(float64(stone))) + 1) / 2
+	divisor := int(math.Pow10(half))
+
+	left := stone / divisor
+	right := stone % divisor
+
+	splitCache[stone] = []int{left, right}
+
+	return left, right
 }
 
-func Part2(stones map[int]int, steps int) int {
+func cacheKey(key Key, value int) int {
+	cache[key] = value
+	return value
+}
+
+func update(stone int, depth int) int {
+	key := Key{depth, stone}
+
+	if count, exists := cache[key]; exists {
+		cacheMisses++
+		return count
+	}
+
+	cacheHits++
+
+	if depth == 0 {
+		return cacheKey(key, 1)
+	}
+
+	if stone == 0 {
+		return cacheKey(key, update(1, depth-1))
+	}
+
+	places := int(math.Log10(float64(stone))) + 1
+	if places%2 == 0 {
+		split1, split2 := split(stone)
+		result := update(split1, depth-1) + update(split2, depth-1)
+		return cacheKey(key, result)
+	}
+
+	return cacheKey(key, update(stone*2024, depth-1))
+}
+
+func Part1(stones []int, steps int) int {
+	result := 0
+	for _, stone := range stones {
+		result += update(stone, steps)
+	}
+
+	return result
+}
+
+func Part2(stones []int, steps int) int {
 	return Part1(stones, steps)
 }
 
@@ -59,7 +90,7 @@ func Run(filename string) (int, int) {
 	}
 	defer file.Close()
 
-	stones := make(map[int]int)
+	stones := []int{}
 
 	scanner := bufio.NewScanner(file)
 	for scanner.Scan() {
@@ -71,7 +102,7 @@ func Run(filename string) (int, int) {
 				panic(err)
 			}
 
-			stones[id] += 1
+			stones = append(stones, id)
 		}
 	}