Bfs.cs

Go to the documentation of this file.

#region License
/*This file is part of Satsuma Graph Library
Copyright © 2013 Balázs Szalkai

This software is provided 'as-is', without any express or implied
warranty. In no event will the authors be held liable for any damages
arising from the use of this software.

Permission is granted to anyone to use this software for any purpose,
including commercial applications, and to alter it and redistribute it
freely, subject to the following restrictions:

   1. The origin of this software must not be misrepresented; you must not
   claim that you wrote the original software. If you use this software
   in a product, an acknowledgment in the product documentation would be
   appreciated but is not required.

   2. Altered source versions must be plainly marked as such, and must not be
   misrepresented as being the original software.

   3. This notice may not be removed or altered from any source
   distribution.*/
#endregion

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Satsuma
{
    public sealed class Bfs
    {
        public IGraph Graph { get; private set; }

        private readonly Dictionary<Node, Arc> parentArc;
        private readonly Dictionary<Node, int> level;
        private readonly Queue<Node> queue;

        public Bfs(IGraph graph)
        {
            Graph = graph;

            parentArc = new Dictionary<Node, Arc>();
            level = new Dictionary<Node, int>();
            queue = new Queue<Node>();
        }

        public void AddSource(Node node)
        {
            if (Reached(node)) return;

            parentArc[node] = Arc.Invalid;
            level[node] = 0;
            queue.Enqueue(node);
        }

        public bool Step(Func<Node, bool> isTarget, out Node reachedTargetNode)
        {
            reachedTargetNode = Node.Invalid;
            if (queue.Count == 0) return false;

            Node node = queue.Dequeue();
            int d = level[node] + 1;
            foreach (var arc in Graph.Arcs(node, ArcFilter.Forward))
            {
                Node child = Graph.Other(arc, node);
                if (parentArc.ContainsKey(child)) continue;

                queue.Enqueue(child);
                level[child] = d;
                parentArc[child] = arc;

                if (isTarget != null && isTarget(child))
                {
                    reachedTargetNode = child;
                    return false;
                }
            }
            return true;
        }

        public void Run()
        {
            Node dummy;
            while (Step(null, out dummy)) ;
        }

        public Node RunUntilReached(Node target)
        {
            if (Reached(target)) return target; // already reached
            Node reachedTargetNode;
            while (Step(node => node == target, out reachedTargetNode)) ;
            return reachedTargetNode;
        }

        public Node RunUntilReached(Func<Node, bool> isTarget)
        {
            Node reachedTargetNode = ReachedNodes.FirstOrDefault(isTarget);
            if (reachedTargetNode != Node.Invalid) return reachedTargetNode; // already reached
            while (Step(isTarget, out reachedTargetNode)) ;
            return reachedTargetNode;
        }

        public bool Reached(Node x)
        {
            return parentArc.ContainsKey(x);
        }

        public IEnumerable<Node> ReachedNodes { get { return parentArc.Keys; } }

        public int GetLevel(Node node)
        {
            int result;
            return level.TryGetValue(node, out result) ? result : -1;
        }

        public Arc GetParentArc(Node node)
        {
            Arc result;
            return parentArc.TryGetValue(node, out result) ? result : Arc.Invalid;
        }

        public IPath GetPath(Node node)
        {
            if (!Reached(node)) return null;

            var result = new Path(Graph);
            result.Begin(node);
            while (true)
            {
                Arc arc = GetParentArc(node);
                if (arc == Arc.Invalid) break;
                result.AddFirst(arc);
                node = Graph.Other(arc, node);
            }
            return result;
        }
    }
}