private void visit(EdgeWightedGraph g, Int32 v)
{
marked[v] = true;
foreach (Edge e in g.Adj(v))
{
int w = e.Other(v);
if (marked[w])
{
continue;//访问过了
}
if (e.Weight < disTo[w])
{
//从MST到w的距离变短了。最佳边变成e
edgeTo[w] = e;
disTo[w] = e.Weight;
if (pq.Contains(w))
{
pq.Change(w, disTo[w]);
}
else
{
pq.Insert(w, disTo[w]);
}
}
}
}
private Chapter2.SortDemos.IndexPriorityQueue <Double> pq; //始终有最短的边
/// <summary>
/// 构造函数
/// </summary>
/// <param name="graph">有向加权非负权图</param>
/// <param name="s">起点</param>
public DijkstraSP(DirectedWeightedGraph graph, int s)
{
edgeTo = new DirectedEdge[graph.V];
disTo = new Double[graph.V];
pq = new Chapter2.SortDemos.IndexPriorityQueue <double>(graph.V);
for (Int32 v = 0; v < graph.V; ++v)
{
disTo[v] = Double.PositiveInfinity;
}
disTo[s] = 0.0;//自己到自己为0
pq.Insert(s, 0.0);
while (!pq.IsEmpty())
{
Relax(graph, pq.DeleteMin());//放松节点，找到到某个点的最短的距离
}
}
private Chapter2.SortDemos.IndexPriorityQueue <Double> pq; //保存最小边的最小堆
public PrimMST(EdgeWightedGraph g)
{
pq = new Chapter2.SortDemos.IndexPriorityQueue <double>(g.V, (Double s, Double b) =>
{
return(s < b);
});//允许的标号[0,g.V]
edgeTo = new Edge[g.V];
marked = new Boolean[g.V];
disTo = new Double[g.V];
for (Int32 v = 0; v < g.V; ++v)
{
disTo[v] = Double.PositiveInfinity; //表示为正无穷
}
pq.Insert(0, 0.0);
disTo[0] = 0.0;
while (!pq.IsEmpty())
{
visit(g, pq.DeleteMin());//获取二叉堆中总是最小的索引
}
}
private void Relax(DirectedWeightedGraph g, int v)
{
foreach (DirectedEdge edge in g.GetEdge(v))
{
int w = edge.End;
//如果存在放松的条件
if (disTo[w] > disTo[v] + edge.Weight)
{
//存在，需要更新
disTo[w] = disTo[v] + edge.Weight;
edgeTo[w] = edge;
//重新累计从 s 到某个点的最短距离。这个距离只有可能减小
if (pq.Contains(w))
{
pq.Change(w, disTo[w]);
}
else
{
pq.Insert(w, disTo[w]);
}
}
}
}
