day22: solve part two

Author: fxnn

day22/example3.txt

@@ -0,0 +1,4 @@
+1
+2
+3
+2024

day22/main.go

@@ -35,15 +35,53 @@ func calculateNextSecret(secret int) int {
 	return step3
 }
 
+type changesHash string
+
+func hashChanges(changes []int) changesHash {
+	return changesHash(fmt.Sprintf("%v", changes))
+}
+
 func main() {
 	var sum int
+	var totalGain = make(map[changesHash]int)
 	for _, initialSecret := range readInitialSecrets() {
 		var secret = initialSecret
+		var changes []int
+		var buyerGain = make(map[changesHash]int)
 		for i := 0; i < 2000; i++ {
+			var oldPrice = secret % 10
 			secret = calculateNextSecret(secret)
+			var price = secret % 10
+			var change = price - oldPrice
+			if len(changes) == 4 {
+				changes = changes[1:4]
+			}
+			changes = append(changes, change)
+			var hash = hashChanges(changes)
+			if _, ok := buyerGain[hash]; !ok {
+				buyerGain[hash] = price
+			}
 		}
 		sum += secret
 		fmt.Printf("%d: %d\n", initialSecret, secret)
+		for hash, price := range buyerGain {
+			var totalPrice int
+			if oldTotalPrice, ok := totalGain[hash]; ok {
+				totalPrice += oldTotalPrice
+			}
+			totalPrice += price
+			totalGain[hash] = totalPrice
+		}
+	}
+	fmt.Printf("sum of 2000th secrets: %d\n", sum)
+
+	var maxHash changesHash
+	var maxPrice int
+	for hash, price := range totalGain {
+		if price > maxPrice {
+			maxHash = hash
+			maxPrice = price
+		}
 	}
-	fmt.Printf("sum of secrets: %d\n", sum)
+	fmt.Printf("max gain is %d for sequence %s\n", maxPrice, maxHash)
 }