stamp.go

package main

import (
	"crypto/md5"
	"fmt"
	"io"
	"math/rand"
	"runtime"
	"time"
)

const pattern = "Hello, James here. %s. I like cupcakes."
const chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz1234567890"

func RandomString(length int, generator *rand.Rand) string {
	ret := ""
	for i := 0; i < length; i++ {
		ret += string(chars[generator.Intn(len(chars))])
	}
	return ret
}

type Stamp struct {
	Attempt string
	Sum     []byte
}

func (s *Stamp) MakeAttempt(generator *rand.Rand) {
	s.Attempt = fmt.Sprintf(pattern, RandomString(15, generator))
	hash := md5.New()
	io.WriteString(hash, s.Attempt)
	s.Sum = hash.Sum(nil)
}

func (s *Stamp) IsValid() bool {
	count := 0
	for _, b := range s.Sum[:3] {
		if b == 0 {
			count++
		}
	}
	return count >= 3
}

func FindStamp(c chan<- *Stamp) {
	source := rand.NewSource(time.Now().UnixNano())
	generator := rand.New(source)

	stamp := new(Stamp)
	for {
		stamp.MakeAttempt(generator)
		if stamp.IsValid() {
			c <- stamp
			return
		}
	}
}

func main() {
	c := make(chan *Stamp)

	num_cpus := runtime.NumCPU()
	runtime.GOMAXPROCS(num_cpus)

	for i := 0; i < num_cpus; i++ {
		go FindStamp(c)
	}

	stamp := <-c

	fmt.Printf("%s\n%x\n", stamp.Attempt, stamp.Sum)
}