From: Steinar H. Gunderson <sesse@samfundet.no>
Date: Fri, 7 Apr 2006 19:56:03 +0000 (+0000)
Subject: Implement a new version of the MST finder (disabled by default).
X-Git-Url: https://git.sesse.net/?a=commitdiff_plain;h=089c57286db1cc0f8f344ca583146f5550fb11d4;hp=8009a5bab6f840576b44a6d70e833c3c2be2a88b;p=nms

Implement a new version of the MST finder (disabled by default).
---

diff --git a/tsp/tsp.cpp b/tsp/tsp.cpp
index 760646c..e7fbab0 100644
--- a/tsp/tsp.cpp
+++ b/tsp/tsp.cpp
@@ -8,6 +8,7 @@
 #define MAX_ROW 75
 #define MIN_SWITCH 1
 #define MAX_SWITCH 6
+#define HEAP_MST 0
 
 static const unsigned num_cache_elem = (MAX_ROW * MAX_SWITCH * 2) * (MAX_ROW * MAX_SWITCH * 2);
 static unsigned short dist_cache[(MAX_ROW * MAX_SWITCH * 2) * (MAX_ROW * MAX_SWITCH * 2)], opt_dist_cache[MAX_ROW * MAX_SWITCH * MAX_ROW * MAX_SWITCH];
@@ -121,6 +122,72 @@ int optimistic_distance(int row_from, int switch_from, int row_to, int switch_to
 		return distance(row_from, switch_from, 0, row_to, switch_to, 0);
 }
 
+#if HEAP_MST
+// this is, surprisingly enough, _slower_ than the naive variant below, so it's not enabled
+struct prim_queue_val {
+	std::pair<unsigned, unsigned> dst;
+	int cost;
+
+	bool operator< (const prim_queue_val &other) const
+	{
+		return (cost > other.cost);
+	}
+};
+
+// standard O(V^2 log v) prim
+int prim_mst(std::set<std::pair<unsigned, unsigned> > &in)
+{
+	std::set<std::pair<unsigned, unsigned> > set2;
+	std::priority_queue<prim_queue_val> queue;
+
+	// pick the first one
+	std::set<std::pair<unsigned, unsigned> >::iterator start = in.begin();
+	
+	unsigned row = start->first;
+	unsigned num = start->second;
+
+	set2.insert(*start);
+	
+	// find all the edges out from it
+	for (std::set<std::pair<unsigned, unsigned> >::iterator j = in.begin(); j != in.end(); ++j) {
+		if (set2.count(*j))
+			continue;
+		
+		unsigned d = opt_cache(row, num, j->first, j->second);
+		prim_queue_val val = { *j, d };
+		queue.push(val);
+	}
+
+	unsigned total_cost = 0;
+	while (set2.size() != in.size()) {
+invalid:
+		prim_queue_val val = queue.top();
+		queue.pop();
+		
+		// check if dst is already moved
+		if (set2.count(val.dst))
+			goto invalid;
+	
+		unsigned row = val.dst.first;
+		unsigned num = val.dst.second;
+		set2.insert(val.dst);
+
+		total_cost += val.cost;
+
+		// find all the edges from this new node
+		for (std::set<std::pair<unsigned, unsigned> >::iterator j = in.begin(); j != in.end(); ++j) {
+			if (set2.count(*j))
+				continue;
+			
+			unsigned d = opt_cache(row, num, j->first, j->second);
+			prim_queue_val val = { *j, d };
+			queue.push(val);
+		}
+	}
+
+	return total_cost;
+}
+#else
 // extremely primitive O(V^3) prim
 int prim_mst(std::set<std::pair<unsigned, unsigned> > &set1)
 {
@@ -153,7 +220,7 @@ int prim_mst(std::set<std::pair<unsigned, unsigned> > &set1)
 
 	return total_cost;
 }
-
+#endif
 
 void print_tour(std::vector<std::pair<unsigned, unsigned> > &points)
 {