subsetsum1(A,k):
|  Input  set A of n integers, target sum k
|  Output true if Σx∈Sx=k for some S⊆A
|         false otherwise
|
|  for s=0..2n-1 do
|  |  if k = Σ(ith bit of s is 1) A[i] then
|  |     return true
|  |  end if
|  end for
|  return false