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[78] | 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& G, NodeIt 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(NodeIt 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_H |
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| 23 | #define REVERSE_BFS_H |
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| 24 | |
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| 25 | #include <queue> |
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| 26 | #include <list_graph.hh> |
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| 27 | |
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| 28 | |
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| 29 | namespace marci { |
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| 30 | |
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| 31 | template <typename Graph> |
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| 32 | class reverse_bfs { |
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| 33 | typedef typename Graph::NodeIt NodeIt; |
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| 34 | typedef typename Graph::EachNodeIt EachNodeIt; |
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| 35 | typedef typename Graph::InEdgeIt InEdgeIt; |
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| 36 | |
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| 37 | |
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| 38 | Graph& G; |
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| 39 | NodeIt t; |
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| 40 | typename Graph::NodeMap<int> distance; |
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| 41 | |
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| 42 | |
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| 43 | public : |
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| 44 | |
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| 45 | /* |
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| 46 | The distance of the Nodes is n, except t for which it is 0. |
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| 47 | */ |
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| 48 | reverse_bfs(Graph& _G, NodeIt _t) : G(_G), t(_t), distance(G, G.nodeNum()) { |
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| 49 | distance.set(t,0); |
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| 50 | } |
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| 51 | |
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| 52 | void run() { |
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| 53 | |
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| 54 | typename Graph::NodeMap<bool> reached(G, false); |
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| 55 | reached.set(t, true); |
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| 56 | |
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| 57 | std::queue<NodeIt> bfs_queue; |
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| 58 | bfs_queue.push(t); |
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| 59 | |
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| 60 | while (!bfs_queue.empty()) { |
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| 61 | |
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| 62 | NodeIt v=bfs_queue.front(); |
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| 63 | bfs_queue.pop(); |
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| 64 | |
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| 65 | for(InEdgeIt e=G.template first<InEdgeIt>(v); e.valid(); ++e) { |
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| 66 | NodeIt w=G.tail(e); |
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| 67 | if (!reached.get(w)) { |
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| 68 | bfs_queue.push(w); |
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| 69 | distance.set(w, distance.get(v)+1); |
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| 70 | reached.set(w, true); |
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| 71 | } |
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| 72 | } |
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| 73 | } |
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| 74 | } |
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| 75 | |
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| 76 | |
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| 77 | |
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| 78 | int dist(NodeIt v) { |
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| 79 | return distance.get(v); |
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| 80 | } |
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| 81 | |
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| 82 | |
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| 83 | }; |
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| 84 | |
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| 85 | } // namespace marci |
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| 86 | |
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| 87 | #endif //REVERSE_BFS_HH |
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| 88 | |
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| 89 | |
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