Longest path problem, including trivial test case generator and solution visualization. Example output: http://chart.googleapis.com/chart?cht=gv:neato&chl=graph{node[shape=circle]35[penwidth=3];56[penwidth=3];23--74;58--69;37--68;17--57;23--67;48--52;28--42;25--34;51--55;11--29;1--26;2--11;7--37;11--42;32--71;13--70;18--60;20--46;4--51;25--30;23…

ripoff.lp

#begin_lua

  function collect(pred,arity)
    local t = {}
    Assignment.begin(pred,arity)
    while Assignment.next() do
      if Assignment.isTrue() then
        table.insert(t,Assignment.args())
      end
    end
    return t
  end

  function onModel()
    local edges = collect("edge",2)
    local chunks = {} 
    table.insert(chunks, "graph{node[shape=circle]")
    for _,e in ipairs(collect("start",1)) do table.insert(chunks, tostring(e[1]).."[penwidth=3];") end
    for _,e in ipairs(collect("finish",1)) do table.insert(chunks, tostring(e[1]).."[penwidth=3];") end
    for _,e in ipairs(collect("vis_edge",2)) do table.insert(chunks, tostring(e[1]).."--"..tostring(e[2])..";") end
    table.insert(chunks,"edge[penwidth=3];")
    for _,e in ipairs(collect("link",2)) do table.insert(chunks, tostring(e[1]).."--"..tostring(e[2])..";") end
    table.insert(chunks,"}")
    local dot = table.concat(chunks,"")
    print("http://chart.googleapis.com/chart?cht=gv:neato&chl="..dot)
  end
 
  math.randomseed(os.time())

  function flip(n,...)
    if math.random() < 1.0/n then
      return 1
    else
      return 0
    end
  end

#end_lua.

#const nodes = 75.
node(1..nodes).
edge(P,Q) :- node(P;Q), @flip(nodes,P,Q)==1.
edge(P,Q) :- edge(Q,P). % edges are bidirectional

1 { start(Node):node(Node) } 1.
1 { finish(Node):node(Node) } 1.

reached(Node) :- start(Node).
1 { link(Node,Peer):edge(Node,Peer) } 1 :- reached(Node), not finish(Node).
reached(Peer) :- link(Node,Peer).

:- finish(N), not reached(N).

#maximize { reached(N) }.

vis_edge(P,Q) :- edge(P,Q), P<Q, not link(P,Q), not link(Q,P).

#hide.
#show start/1.
#show finish/1.
#show link/2.