1 | /* |
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2 | reverse_bfs |
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3 | by jacint |
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4 | Performs a bfs on the out edges. It does not count predecessors, |
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5 | only the distances, but one can easily modify it to know the pred as well. |
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6 | |
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7 | Constructor: |
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8 | |
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9 | reverse_bfs(graph_type& G, node_iterator t) |
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10 | |
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11 | |
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12 | |
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13 | Member functions: |
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14 | |
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15 | void run(): runs a reverse bfs from t |
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16 | |
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17 | The following function should be used after run() was already run. |
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18 | |
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19 | int dist(node_iterator v) : returns the distance from v to t. It is the number of nodes if t is not reachable from v. |
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20 | |
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21 | */ |
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22 | #ifndef REVERSE_BFS_HH |
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23 | #define REVERSE_BFS_HH |
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24 | |
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25 | #include <queue> |
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26 | |
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27 | #include <marci_graph_traits.hh> |
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28 | #include <marci_property_vector.hh> |
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29 | |
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30 | |
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31 | |
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32 | namespace marci { |
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33 | |
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34 | template <typename graph_type> |
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35 | class reverse_bfs { |
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36 | typedef typename graph_traits<graph_type>::node_iterator node_iterator; |
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37 | //typedef typename graph_traits<graph_type>::edge_iterator edge_iterator; |
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38 | typedef typename graph_traits<graph_type>::each_node_iterator each_node_iterator; |
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39 | typedef typename graph_traits<graph_type>::in_edge_iterator in_edge_iterator; |
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40 | |
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41 | |
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42 | graph_type& G; |
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43 | node_iterator t; |
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44 | // node_property_vector<graph_type, edge_iterator> pred; |
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45 | node_property_vector<graph_type, int> distance; |
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46 | |
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47 | |
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48 | public : |
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49 | |
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50 | /* |
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51 | The distance of the nodes is n, except t for which it is 0. |
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52 | */ |
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53 | reverse_bfs(graph_type& _G, node_iterator _t) : G(_G), t(_t), distance(G, number_of(G.first_node())) { |
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54 | distance.put(t,0); |
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55 | } |
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56 | |
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57 | void run() { |
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58 | |
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59 | node_property_vector<graph_type, bool> reached(G, false); |
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60 | reached.put(t, true); |
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61 | |
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62 | std::queue<node_iterator> bfs_queue; |
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63 | bfs_queue.push(t); |
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64 | |
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65 | while (!bfs_queue.empty()) { |
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66 | |
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67 | node_iterator v=bfs_queue.front(); |
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68 | bfs_queue.pop(); |
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69 | |
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70 | for(in_edge_iterator e=G.first_in_edge(v); e.valid(); ++e) { |
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71 | node_iterator w=G.tail(e); |
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72 | if (!reached.get(w)) { |
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73 | bfs_queue.push(w); |
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74 | distance.put(w, distance.get(v)+1); |
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75 | reached.put(w, true); |
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76 | } |
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77 | } |
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78 | } |
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79 | } |
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80 | |
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81 | |
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82 | |
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83 | int dist(node_iterator v) { |
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84 | return distance.get(v); |
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85 | } |
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86 | |
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87 | |
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88 | }; |
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89 | |
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90 | } // namespace marci |
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91 | |
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92 | #endif //REVERSE_BFS_HH |
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93 | |
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94 | |
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