Josephus problem

Iterative:

func josephus(n, k) {
    var prisoners = @^n
    while (prisoners.len > 1) {
        prisoners.rotate!(k - 1).shift
    }
    return prisoners[0]
}

Recursive:

func josephus(n, k) {
    n == 1 ? 0 : ((__FUNC__(n-1, k) + k) % n)
}

Calling the function:

var survivor = josephus(41, 3)
say "Prisoner #{survivor} survived."

Output:

Prisoner 30 survived.