diff --git a/day12/dayTwelve.go b/day12/dayTwelve.go
index c6dc31e..bbf4abb 100644
--- a/day12/dayTwelve.go
+++ b/day12/dayTwelve.go
@@ -55,7 +55,8 @@ func Run() int {
 				blockLengthSum += blockLen
 			}
 
-			variantsCount := generatePermutations("", len(mask), blockLengs, blockLengthSum, mask)
+			memo := make(map[string]int)
+			variantsCount := generatePermutations("", len(mask), blockLengs, blockLengthSum, mask, memo)
 
 			log.Printf("%d : for line %s blocks %+v matches %d\n", lineNum, mask, blockLengs, variantsCount)
 			matches <- variantsCount
@@ -115,7 +116,14 @@ func ReadLine(line string) (string, []int) {
 	return mask, blockLengs
 }
 
-func generatePermutations(curString string, targetLength int, blockLengths []int, blockLengthsSum int, mask string) int {
+func generatePermutations(curString string, targetLength int, blockLengths []int, blockLengthsSum int, mask string, memo map[string]int) int {
+
+	memoKey := fmt.Sprintf("%+v|%d", blockLengths, len(curString))
+	memoized, memoFound := memo[memoKey]
+	if memoFound {
+		return memoized
+	}
+
 	// fmt.Printf("> entering with \n%s\nfor map \n%s\n\n", curString, mask)
 	// time.Sleep(time.Second)
 	if !isVariantMatchesMask(curString, mask) {
@@ -131,6 +139,7 @@ func generatePermutations(curString string, targetLength int, blockLengths []int
 		if !isVariantMatchesMask(variant, mask) {
 			return 0
 		}
+		memo[memoKey] = 1
 		return 1
 	}
 
@@ -150,9 +159,10 @@ func generatePermutations(curString string, targetLength int, blockLengths []int
 	whenPass := curString + "."
 	whenAdd := curString + strings.Repeat("#", nextBlock) + strings.Repeat(".", rightPointRepeat)
 
-	passCount := generatePermutations(whenPass, targetLength, blockLengths, blockLengthsSum, mask)
-	addCount := generatePermutations(whenAdd, targetLength, restBlocks, blockLengthsSum-nextBlock, mask)
+	passCount := generatePermutations(whenPass, targetLength, blockLengths, blockLengthsSum, mask, memo)
+	addCount := generatePermutations(whenAdd, targetLength, restBlocks, blockLengthsSum-nextBlock, mask, memo)
 
+	memo[memoKey] = passCount + addCount
 	return passCount + addCount
 }