2 files changed, 253 insertions, 0 deletions
diff --git a/challenge-162/pokgopun/go/ch-1.go b/challenge-162/pokgopun/go/ch-1.go
new file mode 100644
index 0000000000..3c87b36686
--- /dev/null
+++ b/challenge-162/pokgopun/go/ch-1.go
@@ -0,0 +1,53 @@
+// Write a script to generate the check digit of given ISBN-13 code. Please refer wikipedia for more information.
+package main
+
+import (
+	"errors"
+	"fmt"
+	"os"
+	"regexp"
+	"strconv"
+)
+
+func main() {
+	isbns := []string{"978-0-306-40615-7"}
+	if len(os.Args) > 1 {
+		isbns = os.Args[1:]
+	}
+	for _, v := range isbns {
+		r, err := checkDigit(extractDigits(v))
+		var res string
+		if err != nil {
+			res = "not available due to " + fmt.Sprint(err)
+		} else {
+			res = strconv.Itoa(r)
+		}
+		fmt.Printf("ISBN-13 check digit for %q is %s\n", v, res)
+	}
+}
+
+func extractDigits(str string) (s []int, n int) {
+	str = regexp.MustCompile(`\D`).ReplaceAllLiteralString(str, "")
+	if len(str) > 0 {
+		for _, v := range str {
+			s = append(s, int(v-48))
+		}
+		return s, len(s)
+	}
+	return []int{}, 0
+}
+
+func checkDigit(s []int, n int) (r int, err error) {
+	if n < 12 || n > 13 {
+		return 0, errors.New("invalid input")
+	}
+	for i := 0; i < 12; i += 2 {
+		r += s[i] + 3*s[i+1]
+	}
+	r %= 10
+	r = 10 - r
+	if r == 10 {
+		r = 0
+	}
+	return r, nil
+}
diff --git a/challenge-162/pokgopun/go/ch-2.go b/challenge-162/pokgopun/go/ch-2.go
new file mode 100644
index 0000000000..e60a68d516
--- /dev/null
+++ b/challenge-162/pokgopun/go/ch-2.go
@@ -0,0 +1,200 @@
+package main
+
+import (
+	"fmt"
+	"regexp"
+	"strings"
+)
+
+func main() {
+	pass1, msg1 := "playfair example", "hide the gold in the tree stump"
+	pf1, _ := New(pass1)
+	res1, err := pf1.Encrypt(msg1)
+	fmt.Printf("encrypt(%q, %q) = %q => %t, err => %v\n", pass1, msg1, res1, res1 == "bmodzbxdnabekudmuixmmouvif", err)
+
+	pass2, msg2 := "perl and raku", "siderwrdulfipaarkcrw"
+	pf2, _ := New(pass2)
+	res2, err := pf2.Decrypt(msg2)
+	fmt.Printf("encrypt(%q, %q) = %q => %t, err => %v\n", pass2, msg2, res2, res2 == "thewexeklychallengex", err)
+}
+
+func isLowercaseLetter(s string) bool {
+	re := regexp.MustCompile(`^[a-z]+$`)
+	return re.MatchString(s)
+}
+func lowerCaseAndRemoveSpace(s string) string {
+	return regexp.MustCompile(`\s`).ReplaceAllLiteralString(strings.ToLower(s), "")
+}
+
+func insertX(s string) string {
+	sep := "x"[0]
+	var b strings.Builder
+	var seen byte
+	for _, v := range []byte(s) {
+		if v == seen {
+			b.WriteByte(sep)
+		}
+		b.WriteByte(v)
+		seen = v
+	}
+	if b.Len()%2 != 0 {
+		b.WriteByte(sep)
+	}
+	return b.String()
+}
+
+type inputType int
+
+const (
+	passphrase inputType = iota
+	msg2encrypt
+	msg2decrypt
+)
+
+func (ipt inputType) String() string {
+	switch ipt {
+	case passphrase:
+		return "passphrase"
+	case msg2encrypt:
+		return "msg2encrypt"
+	case msg2decrypt:
+		return "msg2decrypt"
+	default:
+		return "unknown"
+	}
+}
+
+type input struct {
+	val string
+	t   inputType
+}
+
+func newInput(t inputType, s string) (r input, err error) {
+	fname := "newInput"
+	r = input{lowerCaseAndRemoveSpace(s), t}
+	ok := isLowercaseLetter(r.val)
+	switch t {
+	case passphrase:
+		if !ok {
+			return input{}, fmt.Errorf("%v: %v can only contain english and space characters", fname, t)
+		}
+	case msg2encrypt:
+		if !ok {
+			return input{}, fmt.Errorf("%v: %v can only contain english and space characters", fname, t)
+		}
+		r.val = insertX(r.val)
+	case msg2decrypt:
+		if !isLowercaseLetter(strings.ToLower(s)) || len(s)%2 != 0 {
+			return input{}, fmt.Errorf("%v: %v not encrypted by playfair", fname, t)
+		}
+	default:
+		return input{}, fmt.Errorf("%v: inputType %v is not supported", fname, t)
+	}
+	return r, nil
+}
+
+type rowcol struct{ row, col int }
+
+type playfair struct {
+	char2rc map[byte]rowcol
+	chars   [5][5]byte
+}
+
+func (pf playfair) String() (s string) {
+	var b strings.Builder
+	for _, r := range pf.chars {
+		for _, c := range r {
+			fmt.Fprintf(&b, "%2s%v", string(c), pf.char2rc[c])
+		}
+		b.WriteByte("\n"[0])
+	}
+	return b.String()
+}
+
+func (pf playfair) convert(m input) (string, error) {
+	fname := "convert"
+	var o int
+	switch m.t {
+	case msg2encrypt:
+		o = 1
+	case msg2decrypt:
+		o = 4
+	default:
+		return "", fmt.Errorf("%v: only msg2encrypt/msg2decrypt are processed", fname)
+	}
+	b := []byte(m.val)
+	var r strings.Builder
+	for i := 0; i < len(b); i += 2 {
+		x, y := pf.char2rc[b[i]], pf.char2rc[b[i+1]]
+		switch {
+		case x.row == y.row:
+			x.col = (x.col + o) % 5
+			y.col = (y.col + o) % 5
+		case x.col == y.col:
+			x.row = (x.row + o) % 5
+			y.row = (y.row + o) % 5
+		default:
+			x.col, y.col = y.col, x.col
+		}
+		r.Write([]byte{pf.chars[x.row][x.col], pf.chars[y.row][y.col]})
+	}
+	return r.String(), nil
+}
+
+func (pf playfair) Encrypt(s string) (string, error) {
+	msg, err := newInput(msg2encrypt, s)
+	if err != nil {
+		return "", fmt.Errorf("Encrypt: %w", err)
+	}
+	return pf.convert(msg)
+}
+
+func (pf playfair) Decrypt(s string) (string, error) {
+	msg, err := newInput(msg2decrypt, s)
+	if err != nil {
+		return "", fmt.Errorf("Decrypt: %w", err)
+	}
+	return pf.convert(msg)
+}
+
+func chars(start byte, end byte) string {
+	var sb strings.Builder
+	for i := start; i <= end; i++ {
+		sb.WriteByte(i)
+	}
+	return sb.String()
+}
+
+func New(s string) (pf playfair, err error) {
+	fname := "New"
+	pass, err := newInput(passphrase, s)
+	if err != nil {
+		return playfair{}, fmt.Errorf("%v: %w", fname, err)
+	}
+	pf.char2rc = make(map[byte]rowcol, 26)
+	var row, col int
+	for _, b := range []byte(pass.val + chars("a"[0], "z"[0])) {
+		_, ok := pf.char2rc[b]
+		if ok {
+			continue
+		}
+		if b == "i"[0] || b == "j"[0] {
+			for _, k := range []byte("ij") {
+				pf.char2rc[k] = rowcol{row, col}
+			}
+		} else {
+			pf.char2rc[b] = rowcol{row, col}
+		}
+		pf.chars[row][col] = b
+		if col < 4 {
+			col++
+		} else {
+			col = 0
+			row++
+			if row > 4 {
+				break
+			}
+		}
+	}
+	return pf, nil
+}