Edmonds-Karp add source and sink methods

bnb/edmonds_karp.cpp

@@ -8,8 +8,10 @@
 edmonds_karp::edmonds_karp(const graph &g, std::vector<node_id> sources, std::vector<node_id> sinks) 
     : g_(g), sources_(sources), sinks_(sinks) {
 	
-	index_edges();
-	int num_edges = indexed_edges_.size() / 2;
+	// Initial flow value
+	flow_value_ = 0;
+	
+	int num_edges = g_.num_edges();
 
 	// Initialize vectors
 	flow_.assign(num_edges, 0);
@@ -23,32 +25,6 @@ edmonds_karp::edmonds_karp(const graph &g, std::vector<node_id> sources, std::ve
         sources_and_sinks_[t] = -1;
 };
 
-/* Indexes edges of the graph
-Every edge in the graph is mapped to its unique id
-indexed_edges std::map consists of key: pair<node_id, node_id> value: edge_id */
-void edmonds_karp::index_edges() {
-
-	unsigned int num_nodes = g_.num_nodes();
-	unsigned int eid = 0;
-
-	for (node_id u = 1; u <= num_nodes; u++) {
-
-		std::vector<node_id> neighbors = g_.get_adjacency(u);
-
-		for (node_id v : neighbors) {
-			auto node_pair = std::make_pair(u, v);
-			
-			// edge was already listed
-			if (indexed_edges_.count(std::make_pair(v, u)) == 1) {
-				indexed_edges_[node_pair] = indexed_edges_.at(std::make_pair(v, u));
-			
-			} else {
-				indexed_edges_[node_pair] =  eid;
-				eid++;
-			}
-		}
-	}
-}
 
 /* Breadth-first search in the graph from source nodes to sink nodes */
 std::pair<int, node_id> edmonds_karp::bfs(std::vector<unsigned int> &pred) const {
@@ -73,11 +49,17 @@ std::pair<int, node_id> edmonds_karp::bfs(std::vector<unsigned int> &pred) const
 		node_id u = q.front();
 		q.pop();
 
-		std::vector<node_id> neighbors = g_.get_adjacency(u);
+		const std::vector<node_id> & neighbors = g_.get_adjacency(u);
 
 		// iterate through neighbors of u
 		for (node_id v : neighbors) {
-			unsigned int edge_id = indexed_edges_.at(std::make_pair(u, v));
+
+			unsigned int edge_id;
+			if ( u < v )
+				edge_id = g_.get_edge_id(u, v);
+			else 
+				edge_id = g_.get_edge_id(v, u);
+
 			int edge_weight = 1; // unweighted graph
 
 			if (((u >= v && flow_[edge_id] < edge_weight) 
@@ -105,6 +87,20 @@ std::pair<int, node_id> edmonds_karp::bfs(std::vector<unsigned int> &pred) const
 };
 
 
+void edmonds_karp::add_source(node_id s) {
+	sources_.push_back(s);
+	sources_and_sinks_[s] = 1;
+	run();
+}
+
+
+void edmonds_karp::add_sink(node_id t) {
+	sinks_.push_back(t);
+	sources_and_sinks_[t] = -1;
+	run();
+}
+
+
 /* Edmonds-Karp Algorithm for unweighted, undirected graphs
 Step 0: Index graph edges 
 Step 1: Initialize flow and residual flow vectors with length |E|
@@ -114,8 +110,6 @@ Step 3: Add gain that was calculated during BFS to the flow value. Break from th
 Step 4: Update flow and residual flow values for each node */
 void edmonds_karp::run() {
 
-	flow_value_ = 0;
-
 	while (true) {
 		std::vector<node_id> pred;
 
@@ -134,12 +128,13 @@ void edmonds_karp::run() {
 		bool source_reached = false;
 		while (!source_reached) {
 			node_id u = pred[v];
-			int edge_id = indexed_edges_[std::make_pair(u, v)];
 
 			if (u >= v) {
+				unsigned int edge_id = g_.get_edge_id(v, u);
 				flow_[edge_id] += gain;
 				resid_flow_[edge_id] -= gain;
 			} else {
+				unsigned int edge_id = g_.get_edge_id(u, v);
 				flow_[edge_id] -= gain;
 				resid_flow_[edge_id] += gain;
 			}
@@ -153,6 +148,7 @@ void edmonds_karp::run() {
 	
 };
 
+
 int edmonds_karp::get_max_flow() const {
     return flow_value_;
 };

include/gp-bnb/edmonds_karp.hpp

@@ -48,6 +48,13 @@ public:
 	 */
 	void run();
 
+	/**
+	 * Dynamically add a source or a sink node and 
+	 * recalculate maximum flow value
+	 */
+	void add_source(node_id s);
+	void add_sink(node_id t);
+
 	/**
 	 * Returns the value of the maximum flow from source to sink.
 	 *