1 files changed, 93 insertions, 0 deletions
diff --git a/gcd/gcd.go b/gcd/gcd.go
new file mode 100644
index 0000000..562e53b
--- /dev/null
+++ b/gcd/gcd.go
@@ -0,0 +1,93 @@
+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
+		}
+	}
+}