# Pseudo-code

array dflabels[] 
for each node I in graph
  dflables[I] = 0

s := 0
d := 0 # same as "s", which is you
# as recursive
function acyclic (start_node)
  if 1 > dflabels[start_node]# max num visits is 1
    dflabels[start_node]++
    for each i in adjacent_nodes(start_node)
      acyclic(i)    
    end for
    dflabels[start_node]--   # unlike strict dft decrement
  else                       # indicates we've been here before
    if start_node == s       # check if this is YOU
      print "Cycle back to me found!"
    end if
  end if
  return
end function acyclic

# initiate
call acyclic(s)