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package main
import (
"fmt"
"math"
"os"
"strconv"
"sync"
)
func main() {
if len(os.Args) != 3 {
fmt.Println("we need 2 numbers. usage: ./gcd 200 50")
os.Exit(2)
}
a, err := strconv.Atoi(os.Args[1])
if err != nil {
fmt.Printf("whatever %s is… I can't make it an integer: %v\n", os.Args[1], err)
os.Exit(1)
}
b, err := strconv.Atoi(os.Args[2])
if err != nil {
fmt.Printf("whatever %s is… I can't make it an integer: %v\n", os.Args[2], err)
os.Exit(1)
}
fmt.Println(gcd(a, b))
}
func gcd(a, b int) int {
if a == 0 || b == 0 {
return 0
}
adiv := make(chan []int)
bdiv := make(chan []int)
go getDivisors(a, adiv)
go getDivisors(b, bdiv)
adivs := <-adiv
bdivs := <-bdiv
var gcd int
for i := 0; i < len(adivs); i++ {
for j := 0; j < len(bdivs); j++ {
if adivs[i] == bdivs[j] && adivs[i] > gcd {
gcd = adivs[i]
}
}
}
return gcd
}
func getDivisors(num int, out chan []int) {
results := make(chan int, 4096)
joined := make(chan struct{})
var res []int
var wg sync.WaitGroup
go func(r chan int) {
for i := range r {
res = append(res, i)
}
joined <- struct{}{}
}(results)
concurrency := int(math.Ceil(float64(num) / 512))
for i := 0; i < concurrency; i++ {
wg.Add(1)
go func(n, l, u int) {
defer wg.Done()
getDivisorsLimit(n, l, u, results)
}(num, i*512+1, i*512+512)
}
wg.Wait()
close(results)
<-joined
out <- res
}
func getDivisorsLimit(num, lowerBound, upperBound int, results chan int) {
for i := lowerBound; i <= upperBound && i <= num; i++ {
if num%i == 0 {
results <- i
}
}
}
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