biggest-prime-in-number.go

biggest-prime-in-number.go

package main

import (
	"fmt"
	"math"
	"strconv"
	"log"
	"sort"
	"time"
	"errors"
)

type Primes []uint64

func (a Primes ) Len() int           { return len(a) }
func (a Primes ) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }
func (a Primes ) Less(i, j int) bool { return a[i] < a[j] }

func main() {
	//var num uint64 = 1<<64 - 121 -> RIPs the play.golang.org
	defer timeTrack(time.Now(), "main")
	
	nums := [...]uint64{
		5439804848980213812,
		4444444444444444454,
		0,
		4,
		9832197432987498198,
	}
	
	for _, num := range nums {
		checkNumber(num)
	}
}

func checkNumber(num uint64) {
	res, err := getBiggestPrimeInNumber(num)
	
	if err != nil {
   		 fmt.Println(err)
	} else {
	  fmt.Printf("In the number: %d\tthe biggest prime is: %d\n", num, res)
	}
}

func isPrime(value uint64) bool {
	var i uint64;
	for i = 2; i <= uint64(math.Floor(math.Sqrt(float64(value)))); i++ {
		if value % i == 0 {
			return false
		}
	}
	return value > 1
}

func getBiggestPrimeInNumber(num uint64) (res uint64, err error)  {
	defer timeTrack(time.Now(), "getBiggestPrimeInNumber")
	
	if num < 2 {
		log.Fatal("The number should be higher than 1")
	}

	var primes Primes
	numStr := strconv.FormatUint(num, 10)
	strLen := len(numStr)
	
	for i := 0; i <= len(numStr); i++ {
		primes = nil
		
		for j := 0; j < i; j++ {
			slice := numStr[j:strLen-(i-1)+j]
			slicedNum, _ := strconv.ParseUint(slice, 10, 64)
			if isPrime(slicedNum) {
				primes = append(primes, slicedNum)
			}
		}
		
		sort.Sort(primes)
		
		if len(primes) > 0 {		
			return primes[len(primes) - 1], nil
		}
	}
	
	return 0, errors.New("Prime has not been found")
}

func timeTrack(start time.Time, name string) {
    elapsed := time.Since(start)
    fmt.Printf("%s took %s\n", name, elapsed)
}

Next step, use import os and os.Args[1] to make it as a cli :)