/// <summary>
/// Adds the undirected edge <tt>e</tt> to this edge-weighted graph.
/// </summary>
/// <param name="e">e the edge</param>
/// <exception cref="IndexOutOfRangeException">unless both endpoints are between 0 and V-1</exception>
public void AddEdge(EdgeW e)
{
var v = e.Either();
var w = e.Other(v);
ValidateVertex(v);
ValidateVertex(w);
_adj[v].Add(e);
_adj[w].Add(e);
E++;
}
private readonly double _weight; // weight of MST
/// <summary>
/// Compute a minimum spanning tree (or forest) of an edge-weighted graph.
/// </summary>
/// <param name="g">g the edge-weighted graph</param>
public BoruvkaMST(EdgeWeightedGraph g)
{
var uf = new UF(g.V);
// repeat at most log V times or until we have V-1 edges
for (var t = 1; t < g.V && _mst.Size() < 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()
var closest = new EdgeW[g.V];
foreach (var 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 || Less(e, closest[i]))
{
closest[i] = e;
}
if (closest[j] == null || Less(e, closest[j]))
{
closest[j] = e;
}
}
// add newly discovered edges to MST
for (var i = 0; i < g.V; i++)
{
var 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);
}
/// <summary>
/// Initializes a random edge-weighted graph with <tt>V</tt> vertices and <em>E</em> edges.
/// </summary>
/// <param name="v">V the number of vertices</param>
/// <param name="e">E the number of edges</param>
/// <exception cref="ArgumentException">if <tt>V</tt> < 0</exception>
/// <exception cref="ArgumentException">if <tt>E</tt> < 0</exception>
public EdgeWeightedGraph(int v, int e) : this(v)
{
if (e < 0)
{
throw new ArgumentException("Number of edges must be nonnegative");
}
for (var i = 0; i < e; i++)
{
var ve = StdRandom.Uniform(v);
var we = StdRandom.Uniform(v);
var weight = Math.Round(100 * StdRandom.Uniform()) / 100.0;
var edge = new EdgeW(ve, we, weight);
AddEdge(edge);
}
}
/// <summary>
/// relax edge e and update pq if changed
/// </summary>
/// <param name="e"></param>
/// <param name="v"></param>
private void Relax(EdgeW e, int v)
{
var w = e.Other(v);
if (_distTo[w] > _distTo[v] + e.Weight)
{
_distTo[w] = _distTo[v] + e.Weight;
_edgeTo[w] = e;
if (_pq.Contains(w))
{
_pq.DecreaseKey(w, _distTo[w]);
}
else
{
_pq.Insert(w, _distTo[w]);
}
}
}
private readonly Collections.Stack <Integer> _cycle = new Collections.Stack <Integer>(); // Eulerian cycle; null if no such cycle
/// <summary>
/// Computes an Eulerian cycle in the specified graph, if one exists.
/// </summary>
/// <param name="g">g the graph</param>
public EulerianCycle(Graph g)
{
// must have at least one EdgeW
if (g.E == 0)
{
return;
}
// necessary condition: all vertices have even degree
// (this test is needed or it might find an Eulerian path instead of cycle)
for (var v = 0; v < g.V; v++)
{
if (g.Degree(v) % 2 != 0)
{
return;
}
}
// create local view of adjacency lists, to iterate one vertex at a time
// the helper EdgeW data type is used to avoid exploring both copies of an EdgeW v-w
var adj = new Collections.Queue <EdgeW> [g.V];
for (var v = 0; v < g.V; v++)
{
adj[v] = new Collections.Queue <EdgeW>();
}
for (var v = 0; v < g.V; v++)
{
var selfLoops = 0;
foreach (int w in g.Adj(v))
{
// careful with self loops
if (v == w)
{
if (selfLoops % 2 == 0)
{
var e = new EdgeW(v, w, 0);
adj[v].Enqueue(e);
adj[w].Enqueue(e);
}
selfLoops++;
}
else if (v < w)
{
var e = new EdgeW(v, w, 0);
adj[v].Enqueue(e);
adj[w].Enqueue(e);
}
}
}
// initialize Collections.Stack with any non-isolated vertex
var s = NonIsolatedVertex(g);
var stack = new Collections.Stack <Integer>();
stack.Push(s);
// greedily search through EdgeWs in iterative DFS style
_cycle = new Collections.Stack <Integer>();
while (!stack.IsEmpty())
{
int v = stack.Pop();
while (!adj[v].IsEmpty())
{
var edgeW = adj[v].Dequeue();
if (edgeW.IsUsed)
{
continue;
}
edgeW.IsUsed = true;
stack.Push(v);
v = edgeW.Other(v);
}
// push vertex with no more leaving EdgeWs to cycle
_cycle.Push(v);
}
// check if all EdgeWs are used
if (_cycle.Size() != g.E + 1)
{
_cycle = null;
}
//assert certifySolution(G);
}
private readonly Collections.Stack <Integer> _path; // Eulerian path; null if no suh path
/// <summary>
/// Computes an Eulerian path in the specified graph, if one exists.
/// </summary>
/// <param name="g">g the graph</param>
public EulerianPath(Graph g)
{
// find vertex from which to start potential Eulerian path:
// a vertex v with odd degree(v) if it exits;
// otherwise a vertex with degree(v) > 0
var oddDegreeVertices = 0;
var s = NonIsolatedVertex(g);
for (var v = 0; v < g.V; v++)
{
if (g.Degree(v) % 2 != 0)
{
oddDegreeVertices++;
s = v;
}
}
// graph can't have an Eulerian path
// (this condition is needed for correctness)
if (oddDegreeVertices > 2)
{
return;
}
// special case for graph with zero edges (has a degenerate Eulerian path)
if (s == -1)
{
s = 0;
}
// create local view of adjacency lists, to iterate one vertex at a time
// the helper Edge data type is used to avoid exploring both copies of an edge v-w
var adj = new Collections.Queue <EdgeW> [g.V];
for (var v = 0; v < g.V; v++)
{
adj[v] = new Collections.Queue <EdgeW>();
}
for (var v = 0; v < g.V; v++)
{
var selfLoops = 0;
foreach (int w in g.Adj(v))
{
// careful with self loops
if (v == w)
{
if (selfLoops % 2 == 0)
{
var e = new EdgeW(v, w, 0);
adj[v].Enqueue(e);
adj[w].Enqueue(e);
}
selfLoops++;
}
else if (v < w)
{
var e = new EdgeW(v, w, 0);
adj[v].Enqueue(e);
adj[w].Enqueue(e);
}
}
}
// initialize stack with any non-isolated vertex
var stack = new Collections.Stack <Integer>();
stack.Push(s);
// greedily search through edges in iterative DFS style
_path = new Collections.Stack <Integer>();
while (!stack.IsEmpty())
{
int v = stack.Pop();
while (!adj[v].IsEmpty())
{
var edge = adj[v].Dequeue();
if (edge.IsUsed)
{
continue;
}
edge.IsUsed = true;
stack.Push(v);
v = edge.Other(v);
}
// push vertex with no more leaving edges to path
_path.Push(v);
}
// check if all edges are used
if (_path.Size() != g.E + 1)
{
_path = null;
}
//assert certifySolution(G);
}
/// <summary>
/// is the weight of edge e strictly less than that of edge f?
/// </summary>
/// <param name="e"></param>
/// <param name="f"></param>
/// <returns></returns>
private static bool Less(EdgeW e, EdgeW f)
{
return(e.Weight < f.Weight);
}
