如何在 QuickGraph Dijkstra 或 A* 中设置目标顶点

Question

我使用的是 QuickGraph 3.6 版，我找到了函数 SetRootVertex，但没有 SetTagretVertex。我需要这个，因为我正在巨大的图中搜索短路径，这会大大加快程序速度。

有问题的类是 DijkstraShortestPathAlgorithm 和 AStarShortestPathAlgorithm。

Answer 1

我认为不使用事件就没有办法做到这一点。

您可以将必要的代码包装在一个扩展方法中，使事情变得清晰，例如：

public static class Extensions
{
    class AStarWrapper<TVertex, TEdge>
    where TEdge : IEdge<TVertex>
    {
        private TVertex target;
        private AStarShortestPathAlgorithm<TVertex, TEdge> innerAlgorithm;
        public AStarWrapper(AStarShortestPathAlgorithm<TVertex, TEdge> innerAlgo, TVertex root, TVertex target)
        {
            innerAlgorithm = innerAlgo;
            this.innerAlgorithm.SetRootVertex(root);
            this.target = target;
            this.innerAlgorithm.FinishVertex += new VertexAction<TVertex>(innerAlgorithm_FinishVertex);
        }
        void innerAlgorithm_FinishVertex(TVertex vertex)
        {
            if (object.Equals(vertex, target))
                this.innerAlgorithm.Abort();
        }
        public double Compute()
        {
            this.innerAlgorithm.Compute();
            return this.innerAlgorithm.Distances[target];
        }
    }

    public static double ComputeDistanceBetween<TVertex, TEdge>(this AStarShortestPathAlgorithm<TVertex, TEdge> algo, TVertex start, TVertex end)
        where TEdge : IEdge<TVertex>
    {
        var wrap = new AStarWrapper<TVertex, TEdge>(algo, start, end);
        return wrap.Compute();
    }
}

用法：

var g = new BidirectionalGraph<int, IEdge<int>>();

g.AddVerticesAndEdge(new Edge<int>(1, 2));
g.AddVerticesAndEdge(new Edge<int>(2, 3));
g.AddVerticesAndEdge(new Edge<int>(3, 4));
g.AddVerticesAndEdge(new Edge<int>(2, 4));

var astar =new AStarShortestPathAlgorithm<int,IEdge<int>>(g, x => 1.0, x => 0.0);
var dist = astar.ComputeDistanceBetween(2, 4);