(**************************************************************************)
(*  Copyright (C) 2012 Pietro Abate <pietro.abate@pps.jussieu.fr>         *)
(*  Copyright (C) 2012 Johannes Schauer <j.schauer@email.de>              *)
(*                                                                        *)
(*  This library is free software: you can redistribute it and/or modify  *)
(*  it under the terms of the GNU Lesser General Public License as        *)
(*  published by the Free Software Foundation, either version 3 of the    *)
(*  License, or (at your option) any later version.                       *)
(**************************************************************************)

open Graph
open ExtLib
open ExtString

module G = Pack.Digraph

let find_all_cycles_johnson g =
  if not G.is_directed then
    assert false;
    (*  stack of nodes in current path *)
  let path = Stack.create () in
    (* vertex: blocked from search *)
  let blocked = Hashtbl.create 1023 in
    (* graph portions that yield no elementary circuit *)
  let b = Hashtbl.create 1023 in
    (* list to accumulate the circuits found  *)
  let result = ref [] in

  let rec unblock n =
    if Hashtbl.find blocked n then begin
      Hashtbl.replace blocked n false;
      List.iter unblock (Hashtbl.find b n);
      Hashtbl.replace b n [];
    end
  in

  let stack_to_list s = 
    let l = ref [] in
    Stack.iter (fun e -> l:= e::!l) s;
    !l
  in

  let rec circuit thisnode startnode component = 
    let closed = ref false in
    Stack.push thisnode path;
    Hashtbl.replace blocked thisnode true;
    G.iter_succ (fun nextnode ->
      if G.V.equal nextnode startnode then begin
        result := ((stack_to_list path))::!result;
        closed := true;
      end else begin if not(Hashtbl.find blocked nextnode) then
        if circuit nextnode startnode component then begin
          closed := true;
        end
      end
    ) component thisnode;
    if !closed then begin
      unblock thisnode
    end
    else
      G.iter_succ (fun nextnode ->
        let l = Hashtbl.find b nextnode in
        if not(List.mem thisnode l) then
          Hashtbl.replace b nextnode (thisnode::l)
      ) component thisnode;
    ignore(Stack.pop path);
    !closed
  in
  let module SV = Set.Make(G.V) in
  let extract_subgraph g s =
    let sg = G.create () in
    List.iter (fun v1 ->
      G.add_vertex sg v1;
      List.iter (fun e ->
        let v2 = G.E.dst e in
        if List.mem v2 s then
          G.add_edge_e sg e
      ) (G.succ_e g v1)
    ) s;
    sg
  in
 (* Johnson's algorithm requires some ordering of the nodes. 
  * They might not be sortable so we assign an arbitrary ordering. 
  *)
  let scc_with_vertex g v =
    let _,scc = G.Components.scc g in
    let n = scc v in
    let sg = G.create () in
    G.iter_vertex (fun v1 ->
      if (scc v1) = n then
        List.iter (fun e ->
          if scc (G.E.dst e) = n then
            G.add_edge_e sg e
        ) (G.succ_e g v1)
    ) g;
    sg
  in

  let list_min = function
    | [] -> invalid_arg "empty list"
    | h::tl -> List.fold_left min h tl
  in

  let sort_components a b =
    compare (list_min a) (list_min b)
  in

  let non_degenerate_scc = List.filter (fun scc -> (List.length scc) > 1) (G.Components.scc_list g) in

  let non_degenerate_subgraphs = List.map
    (fun scc -> extract_subgraph g scc)
    (List.sort ~cmp:sort_components non_degenerate_scc)
  in

  List.iter (fun g ->
    let vertex_set = G.fold_vertex (fun v l -> v::l) g [] in
    List.iter (fun s ->
      let component = scc_with_vertex g s in
      if G.nb_edges component > 0 then begin
        G.iter_vertex (fun node ->
          Hashtbl.replace blocked node false;
          Hashtbl.replace b node [];
        ) component;
        ignore(circuit s s component);
      end;
      G.remove_vertex g s;
    ) (List.sort vertex_set);
  ) non_degenerate_subgraphs;

  List.rev !result
;;

if Array.length Sys.argv != 2 then begin
  Printf.printf "usage: echo \"v1 v2\nv1 v3\n...\" | %s num_vertices\n" Sys.argv.(0);
  exit 1;
end;

let v = int_of_string (Sys.argv.(1)) in
let g = G.create ~size:v () in

let a = Array.init v G.V.create in

try
 while true do
   let v1, v2 = String.split (read_line ()) " " in
   G.add_edge g a.(int_of_string v1) a.(int_of_string v2);
 done;
with End_of_file -> ();

let ll = find_all_cycles_johnson g in
List.iter (fun path ->
  Printf.printf "%s\n" 
  (String.join " " (List.map (fun e -> string_of_int (G.V.label e)) path))
) ll