solve day 3 part 2

2024/day03.go

@@ -24,5 +24,26 @@ func (d Day3) Part1(r io.Reader) string {
 }
 
 func (d Day3) Part2(r io.Reader) string {
-	return ""
+	var bd strings.Builder
+	var sum int
+	io.Copy(&bd, r)
+
+	re := regexp.MustCompile(`mul\((\d{1,3}),(\d{1,3})\)|do\(\)|don\'t\(\)`)
+
+	matches := re.FindAllStringSubmatch(bd.String(), -1)
+
+	var skip bool
+	for _, match := range matches {
+		switch match[0] {
+		case "do()":
+			skip = false
+		case "don't()":
+			skip = true
+		default:
+			if !skip {
+				sum += atoi(match[1]) * atoi(match[2])
+			}
+		}
+	}
+	return printi(sum)
 }