// Output the k! permutations of A in which the first k elements are permuted in all ways.
// To get all permutations of A, use k := length of A.
//
// If k > length of A, will try to access A out of bounds.
// If k <= 0 there will be no output (empty array has no permutations)
procedure permutations(k : integer, A : array of any):
    if k = 1 then
        output(A)
    else
        // permutations with last element fixed
        permutations(k - 1, A)
        // permutations with last element swapped out
        for i := 0; i < k-1; i += 1 do
            if k is even then
                swap(A[i], A[k-1])
            else
                swap(A[0], A[k-1])
            end if
            permutations(k - 1, A)
        end for
    end if