day3, part2

day3/day-three.go

@@ -24,14 +24,16 @@ func Run() int {
 		fmt.Println(num)
 	}
 
-	partNumbersSum := 0
+	// partNumbersSum := 0
-	for _, num := range numbers {
+	// for _, num := range numbers {
-		if len(num.Specials) > 0 {
+	// 	if len(num.Specials) > 0 {
-			partNumbersSum += num.Num
+	// 		partNumbersSum += num.Num
-		}
+	// 	}
-	}
+	// }
 
-	return partNumbersSum
+	gearRatiosSum := partTwo(numbers)
+
+	return gearRatiosSum
 }
 
 type Matrix [][]rune
@@ -135,3 +137,27 @@ func isValidCoord(x, y int, m *Matrix) bool {
 	}
 	return true
 }
+
+// part 2 - find all gears '*' that connect exactly two numbers
+// multiply the numbers and calculate total sum
+// i guess i could do full scan of my numbers?
+// every time i encounter '*' in special symbols, could put that into map, hopefully?
+// with value for the number
+
+func partTwo(numbers []MatrixNumber) int {
+	res := 0
+	specialsMap := make(map[SpecialSymbol][]MatrixNumber)
+	for _, num := range numbers {
+		for special, _ := range num.Specials {
+			specialsMap[special] = append(specialsMap[special], num)
+		}
+	}
+
+	for special, nums := range specialsMap {
+		if special.Symb == '*' && len(nums) == 2 {
+			res += nums[0].Num * nums[1].Num
+		}
+	}
+
+	return res
+}