My answer to rot13

stream.go

// my answer: https://tour.golang.org/methods/23
// their answer: https://github.com/golang/tour/blob/master/solutions/rot13.go

package main

import (
	"io"
	"os"
	"strings"
	"bytes"
)

type rot13Reader struct {
	r io.Reader
}

func (mr rot13Reader) Read(b []byte) (int, error) {
	alpha := []byte("ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz")
	rot13 := []byte("NOPQRSTUVWXYZABCDEFGHIJKLMnopqrstuvwxyzabcdefghijklm")
	
	n, err := mr.r.Read(b)
	for index, value := range b {
		alphaIndex := bytes.IndexByte(alpha, value)
		if alphaIndex > 0 {
			b[index] = rot13[alphaIndex]
		}
	}
	
	return n, err

}


func main() {
	s := strings.NewReader("Lbh penpxrq gur pbqr!")
	r := rot13Reader{s}
	io.Copy(os.Stdout, &r)
}