Compress_LempelZivWelch

Compress_LempelZivWelch.go

package main

import (
	"fmt"
	"strings"
)

var (
	input = "booop"
)

func main() {
	res, dic := LZWComp([]byte(input))
	fmt.Println("result = ", res)

	var revertDic = make(map[string]string)
	for k, v := range dic {
		revertDic[v] = k
	}

	compressed := strings.Split(res, " ")
	deComp := LZWDecomp(compressed, revertDic)

	fmt.Println("decomp =", deComp)
	fmt.Println("input == deComp:", input == deComp)
}

func LZWComp(in []byte) (string, map[string]string) {
	fmt.Println("-----compress-----")
	var (
		w       []byte
		dic         = make(map[string]string)
		counter int = 100
		res     string
	)
	w = append(w, in[0])

	for i := 1; i < len(in); i++ {
		tmp := append(w, in[i])
		_, ok := dic[string(tmp)]
		if ok {
			w = append(w, in[i])
			continue
		}
		dic[string(tmp)] = fmt.Sprintf("%d", counter)
		counter++
		if len(w) == 1 {
			res += string(w) + " "
		} else {
			res += dic[string(w)] + " "
		}

		w = []byte{in[i]}
	}
	res += string(w)
	fmt.Println("dictionary")
	for k, v := range dic {
		fmt.Printf("%-5s = %s\n", k, v)
	}

	return res, dic
}

func LZWDecomp(in []string, dic map[string]string) string {
	fmt.Println("-----decompress-----")
	var (
		w   string
		res string
	)
	res += in[0]
	w += in[0]

	fmt.Printf("in:  %s\nw:   %s\nout: %s\n----\n", in[0], w, res)

	for i := 1; i < len(in); i++ {
		v, ok := dic[in[i]]
		if ok {
			entry := v
			res += entry
			dic[w+string(entry[0])] = w + string(entry[0])
			w = entry
			fmt.Printf("in:  %s\nw:   %s\nout: %s\n----\n", in[i], w, res)
			continue
		}

		if len(in[i]) == 1 {
			entry := in[i]
			res += entry
			dic[w+string(entry[0])] = w + string(entry[0])
			w = entry
			fmt.Printf("in:  %s\nw:   %s\nout: %s\n----\n", in[i], w, res)
			continue
		}

		entry := w + string(w[0])
		res += entry
		dic[entry] = entry
		w = entry
		fmt.Printf("in:  %s\nw:   %s\nout: %s\n----\n", in[i], w, res)
	}
	fmt.Println("dictionary")
	for k, v := range dic {
		fmt.Printf("%-5s = %s\n", k, v)
	}

	return res
}