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[smlnj] View of /MLRISC/trunk/graphs/graph-is-cyclic.sml
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View of /MLRISC/trunk/graphs/graph-is-cyclic.sml

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Revision 2126 - (download) (annotate)
Thu Nov 2 16:11:29 2006 UTC (12 years, 11 months ago) by blume
File size: 748 byte(s)
moved MLRISC to toplevel
(*
 * Tests if a graph is cyclic
 *
 * -- Allen
 *)

structure GraphIsCyclic : GRAPH_IS_CYCLIC = 
struct

   structure G = Graph

   exception Cyclic

   (*
    * Cyclic test
    *)
   fun is_cyclic (G.GRAPH G) = 
   let val N       = #capacity G () 
       val visited = BitSet.create N
       val done    = BitSet.create N
       fun dfs i =
          if BitSet.markAndTest(visited,i) then
             if BitSet.contains(done,i) then ()
             else raise Cyclic
          else 
             (dfsSucc(#out_edges G i);
              BitSet.set(done,i))
       and dfs'(i,_) = dfs i
       and dfsSucc [] = ()
         | dfsSucc((_,j,_)::es) = (dfs j; dfsSucc es)
   in
       (#forall_nodes G dfs'; false) handle Cyclic => true
   end

end


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