beoba

  Out = []
  for a in A:
    for b in B:
      if a == b and !Out.contains(b)://O(n) list search
        Out.append(b)
  return Out

  Out = []
  sort(A)
  sort(B)
  b = 0
  for a in xrange(len(A)):
    vala = A[a]
    valb = B[b]
    if vala == valb:
      Out.append(vala)
      ++a
      ++b
    elif vala < valb:
      ++a
    else://vala > valb
      ++b
  return Out

  Out_set = set([])
  A_set = set([a in A])
  for b in B:
    if A_set.contains(b)://O(1) set search
      Out_set.append(b)
  return list(Out_set)//optional, could return Out_set