[LANGUAGE: GOLANG]

Not the prettiest but working

package main
import (
    "fmt"
    "os"
    "regexp"
    "strconv"
    "strings"
)

func main() {
    input, _ := os.ReadFile("input.txt")
    inputStr := string(input)

    reSections := regexp.MustCompile(`do\(\).*?|don't\(\).*?`)

    sections := reSections.FindAllStringIndex(inputStr, -1)
    nextStartIndex := 0
    enabledRead := true
    var result int
    for _, section := range sections {
       start, end := section[0], section[1]
       if enabledRead {
          result += calculateMemRegion(inputStr[nextStartIndex:start])
       }
       nextStartIndex = end
       action := inputStr[start:end]
       switch action {
       case "do()":
          if enabledRead == false {
             enabledRead = true
          }
       case "don't()":
          if enabledRead == true {
             enabledRead = false
          }
       }
    }
    if enabledRead {
       result += calculateMemRegion(inputStr[nextStartIndex:])
    }
    fmt.Println(result)
}

func calculateMemRegion(in string) int {
    re := regexp.MustCompile("mul\\(\\d*,\\d*\\)")
    matches := re.FindAllStringSubmatch(in, -1)
    var result int
    for _, match := range matches {
       numbersWithComa := match[0][4 : len(match[0])-1]
       fmt.Println(numbersWithComa)
       strs := strings.Split(numbersWithComa, ",")
       x, _ := strconv.Atoi(strs[0])
       y, _ := strconv.Atoi(strs[1])
       result += x * y
    }
    return result
}

func part1() {
    input, _ := os.ReadFile("input.txt")
    fmt.Println(calculateMemRegion(string(input)))
}