private Queue <Edge> mst = new Queue <Edge>(); // edges in MST
/**
* Compute a minimum spanning tree (or forest) of an edge-weighted graph.
* @param G the edge-weighted graph
*/
public KruskalMST(EdgeWeightedGraph G)
{
// more efficient to build heap by passing array of edges
MinPQ <Edge> pq = new MinPQ <Edge>();
foreach (Edge e in G.Edges)
{
pq.Insert(e);
}
// run greedy algorithm
UF uf = new UF(G.V);
while (!pq.IsEmpty && mst.Size < G.V - 1)
{
Edge e = pq.DeleteMin();
int v = e.Either;
int w = e.other(v);
if (!uf.Connected(v, w))
{ // v-w does not create a cycle
// merge v and w components
uf.Union(v, w);
mst.Enqueue(e); // add edge e to mst
weight += e.Weight;
}
}
// check optimality conditions
//assert ;
Contract.Assert(check(G));
}
/**
* Compute a minimum spanning tree (or forest) of an edge-weighted graph.
* @param G the edge-weighted graph
*/
public BoruvkaMST(EdgeWeightedGraph G)
{
UF uf = new UF(G.V);
// repeat at most log V times or until we have V-1 edges
for (int t = 1; t < G.V && mst.Count < G.V - 1; t = t + t)
{
// foreach tree in forest, Find closest edge
// if edge weights are equal, ties are broken in favor of first edge in G.edges()
Edge[] closest = new Edge[G.V];
foreach (Edge e in G.Edges)
{
int v = e.Either, w = e.other(v);
int i = uf.Find(v), j = uf.Find(w);
if (i == j)
{
continue; // same tree
}
if (closest[i] == null || e < closest[i])
{
closest[i] = e;
}
if (closest[j] == null || e < closest[j])
{
closest[j] = e;
}
}
// add newly discovered edges to MST
for (int i = 0; i < G.V; i++)
{
Edge e = closest[i];
if (e != null)
{
int v = e.Either, w = e.other(v);
// don't add the same edge twice
if (!uf.Connected(v, w))
{
mst.Add(e);
Weight += e.Weight;
uf.Union(v, w);
}
}
}
}
// check optimality conditions
//assert check(G);
Contract.Assert(check(G));
}
public void OptimalAlgorithm_UF_StepByStep_Tuples()
{
UF uF = new UF(10);
for (int i = 0; i < 10; i++)
{
int p = tuples[i, 0];
int q = tuples[i, 1];
if (!uF.Connected(p, q))
{
uF.Union(p, q);
}
switch (i)
{
case 0:
Assert.True(uF.Connected(4, 3));
Assert.Equal(4, uF.Ids[3]);
Assert.Equal(1, uF.Ranks[4]);
Assert.Equal(0, uF.Ranks[3]);
break;
case 1:
Assert.True(uF.Connected(8, 3));
Assert.True(uF.Connected(8, 4));
Assert.Equal(4, uF.Ids[3]);
Assert.Equal(4, uF.Ids[8]);
Assert.Equal(1, uF.Ranks[4]);
Assert.Equal(0, uF.Ranks[8]);
break;
case 2:
Assert.True(uF.Connected(6, 5));
Assert.Equal(6, uF.Ids[5]);
Assert.Equal(1, uF.Ranks[6]);
Assert.Equal(0, uF.Ranks[5]);
break;
case 3:
Assert.True(uF.Connected(4, 9));
Assert.Equal(4, uF.Ids[9]);
Assert.Equal(1, uF.Ranks[4]);
Assert.Equal(0, uF.Ranks[9]);
break;
case 4:
Assert.True(uF.Connected(2, 1));
Assert.Equal(2, uF.Ids[1]);
Assert.Equal(1, uF.Ranks[2]);
Assert.Equal(0, uF.Ranks[1]);
break;
case 5:
Assert.True(uF.Connected(8, 9));
Assert.Equal(4, uF.Ids[9]);
Assert.Equal(4, uF.Ids[8]);
break;
case 6:
Assert.True(uF.Connected(5, 0));
Assert.Equal(6, uF.Ids[5]);
Assert.Equal(6, uF.Ids[0]);
break;
case 7:
Assert.True(uF.Connected(7, 2));
Assert.Equal(2, uF.Ids[7]);
break;
case 8:
Assert.True(uF.Connected(6, 1));
Assert.Equal(6, uF.Ids[1]);
Assert.Equal(2, uF.Ranks[6]);
break;
case 9:
Assert.True(uF.Connected(7, 3));
Assert.Equal(6, uF.Ids[4]);
Assert.Equal(6, uF.Ids[7]);
Assert.Equal(6, uF.Ids[3]);
break;
default: break;
}
}
// at the end
Assert.Equal(new byte[] { 0, 0, 1, 0, 1, 0, 2, 0, 0, 0 }, uF.Ranks);
Assert.Equal(new[] { 6, 6, 6, 6, 6, 6, 6, 6, 4, 4 }, uF.Ids);
Assert.Equal(1, uF.Count);
}
