CypherCore/Source/Framework/Algorithms/EdgeWeightedDigraph.cs

using System;
using System.Collections.Generic;
using System.Text;

namespace Framework.Collections
{
    /// <summary>
    /// The EdgeWeightedDigrpah class represents an edge-weighted directed graph of vertices named 0 through V-1, where each directed edge
    /// is of type DirectedEdge and has real-valued weight.
    /// </summary>
    /// <seealso href="http://algs4.cs.princeton.edu/44sp/EdgeWeightedDigraph.java.html">EdgeWeightedDigraph class from Princeton University's Java Algorithms</seealso>
    public class EdgeWeightedDigraph
    {
        private readonly LinkedList<DirectedEdge>[] _adjacent;
        /// <summary>
        /// Constructs an empty edge-weighted digraph with the specified number of vertices and 0 edges
        /// </summary>
        /// <param name="vertices">Number of vertices in the Graph</param>
        public EdgeWeightedDigraph(int vertices)
        {
            NumberOfVertices = vertices;
            NumberOfEdges = 0;
            _adjacent = new LinkedList<DirectedEdge>[NumberOfVertices];
            for (int v = 0; v < NumberOfVertices; v++)
            {
                _adjacent[v] = new LinkedList<DirectedEdge>();
            }
        }
        /// <summary>
        /// The number of vertices in the edge-weighted digraph
        /// </summary>
        public int NumberOfVertices { get; private set; }
        /// <summary>
        /// The number of edges in the edge-weighted digraph
        /// </summary>
        public int NumberOfEdges { get; private set; }
        /// <summary>
        /// Adds the specified directed edge to the edge-weighted digraph
        /// </summary>
        /// <param name="edge">The DirectedEdge to add</param>
        /// <exception cref="ArgumentNullException">DirectedEdge cannot be null</exception>
        public void AddEdge(DirectedEdge edge)
        {
            if (edge == null)
            {
                throw new ArgumentNullException("edge", "DirectedEdge cannot be null");
            }

            _adjacent[edge.From].AddLast(edge);
        }
        /// <summary>
        /// Returns an IEnumerable of the DirectedEdges incident from the specified vertex
        /// </summary>
        /// <param name="vertex">The vertex to find incident DirectedEdges from</param>
        /// <returns>IEnumerable of the DirectedEdges incident from the specified vertex</returns>
        public IEnumerable<DirectedEdge> Adjacent(int vertex)
        {
            return _adjacent[vertex];
        }
        /// <summary>
        /// Returns an IEnumerable of all directed edges in the edge-weighted digraph
        /// </summary>
        /// <returns>IEnumerable of of all directed edges in the edge-weighted digraph</returns>
        public IEnumerable<DirectedEdge> Edges()
        {
            for (int v = 0; v < NumberOfVertices; v++)
            {
                foreach (DirectedEdge edge in _adjacent[v])
                {
                    yield return edge;
                }
            }
        }
        /// <summary>
        /// Returns the number of directed edges incident from the specified vertex
        /// This is known as the outdegree of the vertex
        /// </summary>
        /// <param name="vertex">The vertex to find find the outdegree of</param>
        /// <returns>The number of directed edges incident from the specified vertex</returns>
        public int OutDegree(int vertex)
        {
            return _adjacent[vertex].Count;
        }
        /// <summary>
        /// Returns a string that represents the current edge-weighted digraph
        /// </summary>
        /// <returns>
        /// A string that represents the current edge-weighted digraph
        /// </returns>
        public override string ToString()
        {
            var formattedString = new StringBuilder();
            formattedString.AppendFormat("{0} vertices, {1} edges {2}", NumberOfVertices, NumberOfEdges, Environment.NewLine);
            for (int v = 0; v < NumberOfVertices; v++)
            {
                formattedString.AppendFormat("{0}: ", v);
                foreach (DirectedEdge edge in _adjacent[v])
                {
                    formattedString.AppendFormat("{0} ", edge.To);
                }
                formattedString.AppendLine();
            }
            return formattedString.ToString();
        }
    }

    /// <summary>
    /// The DirectedEdge class represents a weighted edge in an edge-weighted directed graph. 
    /// </summary>
    /// <seealso href="http://algs4.cs.princeton.edu/44sp/DirectedEdge.java.html">DirectedEdge class from Princeton University's Java Algorithms</seealso>
    public class DirectedEdge
    {
        /// <summary>
        /// Constructs a directed edge from one specified vertex to another with the given weight
        /// </summary>
        /// <param name="from">The start vertex</param>
        /// <param name="to">The destination vertex</param>
        /// <param name="weight">The weight of the DirectedEdge</param>
        public DirectedEdge(uint from, uint to, double weight)
        {
            From = from;
            To = to;
            Weight = weight;
        }
        /// <summary>
        /// Returns the destination vertex of the DirectedEdge
        /// </summary>
        public uint From { get; private set; }
        /// <summary>
        /// Returns the start vertex of the DirectedEdge
        /// </summary>
        public uint To { get; private set; }
        /// <summary>
        /// Returns the weight of the DirectedEdge
        /// </summary>
        public double Weight { get; private set; }
        /// <summary>
        /// Returns a string that represents the current DirectedEdge
        /// </summary>
        /// <returns>
        /// A string that represents the current DirectedEdge
        /// </returns>
        public override string ToString()
        {
            return $"From: {From}, To: {To}, Weight: {Weight}";
        }
    }
}