main.go

package main
import "io/ioutil"
import "regexp"
import "log"
import "strings"
import "encoding/json"

func main() {
	size := 4
	mapping := make(map[string]int)
	bytes, err := ioutil.ReadFile("input.txt");
	if err != nil  {
		log.Fatal("Error reading file!")
	}
	value := string(bytes)
	value = standardizeSpaces(value)
	reg, err := regexp.Compile("[^a-zA-Z!?. ]+")
    if err != nil {
        log.Fatal(err)
    }
	processedString := reg.ReplaceAllString(strings.ToLower(value), "")
	sentences := regexp.MustCompile("[!.?]").Split(processedString, -1)
	for _, str := range sentences {
		stringSlice := append([]string{"*BEGIN*"}, strings.Fields(str)...)
		stringSlice = append(stringSlice, "*END*")
		for i := 0; i <= len(stringSlice) - (size * 2); i += 1 {
			key := strings.Join(stringSlice[i:i+size], "_") + "#" + strings.Join(stringSlice[i+size:i+size*2], "_")
			mapping[key] += 1
		}
	}
	if jsonBytes, err := json.Marshal(mapping); err == nil {
		ioutil.WriteFile("output.json", jsonBytes, 0644)
	}
}

func standardizeSpaces(s string) string {
    return strings.Join(strings.Fields(s), " ")
}