If you want to find all "circles of friends," i.e., all cycles to which you are a member, then you need to use a modified depth first traversal algorithm that begins and ends with you.

It is similar to finding all acyclic s-d paths, except in your case s and d (source and destination) are the same - you.

The algorithm is fast, especially if you don't have many friends - like most perl hackers :). 
# 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)

[download]
Of course, the above pseudo-code doesn't facilitate storing the actual paths, this is easily done using input and output parameters. Hope that helps.

In reply to Re: OT(ish) - Best Search Algorithm by perlfan
in thread OT(ish) - Best Search Algorithm by Melly

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