How could I display the route found in my Dijkstra algorithm?

Question

My code runs Dijkstra's algorithm on an adjacency matrix which currently outputs the distance from the given source node to every other node in the graph. However, I am trying to now make it output the route that the algorithm has taken for each result but I'm not sure how I would go about this?

I may also change the code to instead only output the desired route as well instead of all the combinations to make the code a bit more efficient.

using System;

namespace Dijkstra
{
    class Program
    {
        static void Main(string[] args)
        {    
            int[,] graph = {
            //A  B  C  D  E  F  G  H  I  J  K
            { 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 0  }, //A
            { 1, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0  }, //B
            { 0, 0, 0, 1, 0, 0, 1, 0, 0, 0, 0  }, //C
            { 0, 1, 1, 0, 0, 1, 0, 0, 0, 0, 0  }, //D
            { 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0  }, //E
            { 0, 0, 0, 1, 0, 0, 0, 0, 1, 0, 1  }, //F
            { 0, 0, 1, 0, 0, 0, 0, 0, 0, 1, 0  }, //G
            { 1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0  }, //H
            { 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0  }, //I
            { 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0  }, //J
            { 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0  } //K
};

            Dijkstra(graph, 0, 11);
        }

        private static int MinimumDistance(int[] distance, bool[] shortestPathTreeSet, int verticesCount)
        {
            int min = int.MaxValue;
            int minIndex = 0;

            for (int v = 0; v < verticesCount; ++v)
            {
                if (shortestPathTreeSet[v] == false && distance[v] <= min)
                {
                    min = distance[v];
                    minIndex = v;
                }
            }

            return minIndex;
        }

        private static void Print(int[] distance, int verticesCount)
        {
            Console.WriteLine("Vertex    Distance from source");

            for (int i = 0; i < verticesCount; ++i)
                Console.WriteLine("{0}\t  {1}", i, distance[i]);
        }

        public static void Dijkstra(int[,] graph, int source, int verticesCount)
        {
            int[] distance = new int[verticesCount]; // Integer array, size of number of verticies
            bool[] shortestPathTreeSet = new bool[verticesCount]; // boolean array size of number of verticies

            for (int i = 0; i < verticesCount; ++i)     // For every verticy, set the verticy distance to infinite (max int value)
            {
                distance[i] = int.MaxValue;
                shortestPathTreeSet[i] = false;
            }

            distance[source] = 0;   // Distance of source verticie is 0

            for (int count = 0; count < verticesCount - 1; ++count)
            {
                int u = MinimumDistance(distance, shortestPathTreeSet, verticesCount);
                shortestPathTreeSet[u] = true;

                for (int v = 0; v < verticesCount; ++v)
                    if (!shortestPathTreeSet[v] && Convert.ToBoolean(graph[u, v]) && distance[u] != int.MaxValue && distance[u] + graph[u, v] < distance[v])
                        distance[v] = distance[u] + graph[u, v];
            }

            Print(distance, verticesCount);
        }

    }
}

Not sure if exact dupe or not, since the answer is pretty much the same as [what to do for BFS](https://stackoverflow.com/q/9590299/572670). — amit, Aug 02 '22 at 14:41

score 1 · Answer 1 · answered Aug 02 '22 at 14:09

As you update the distance for a vertex, you can also store it's prev vertex - the vertex that led you to the current vertex. Then, once you are done, you can easily trace your steps back to the starting vertex, recursively and store them in a list.

Edit: Do you mean to say you want the path taken to EVERY vertex in the graph?

How could I display the route found in my Dijkstra algorithm?

1 Answers1