advent_day_4.go

// http://adventofcode.com/day/4
// key should be passed on the command line as the first argument
// number of leading zeroes is the second argument
package main

import "crypto/md5"
import "fmt"
import "os"
import "strconv"
import "strings"

func main() {
  key := os.Args[1]
  leading_zeroes, _ := strconv.Atoi(os.Args[2])
  comparison := strings.Repeat("0", leading_zeroes)

  // loop infinitely until we find an MD5 string that has so many leading zeroes
  count := 0

  for {
    // let us know that this is running
    if count % 10000 == 0 {
      fmt.Printf(".")
    }

    // concatenate the key and the value
    test := key + strconv.Itoa(count)

    // determine the MD5 sum as a byte array
    md5sum := md5.Sum([]byte(test))

    // convert the byte array to a string
    md5string := fmt.Sprintf("%x", md5sum)

    // compare and break if we find a match
    if md5string[:leading_zeroes] == comparison {
      fmt.Printf("\n%d: %x\n", count, md5sum)
      break
    }

    count += 1
  }
}