Binary search (stdlib).go

func main() {
    a := []int{1, 3, 6, 10, 15, 21, 28, 36, 45, 55}
    x := 6


    i := sort.Search(len(a), func(i int) bool { return a[i] >= x })
    if i < len(a) && a[i] == x {
        fmt.Printf("found %d at index %d in %v\n", x, i, a)
    } else {
        fmt.Printf("%d not found in %v\n", x, a)
    }
}