Dijkstra algorithm - Java Data Structure

Java examples for Data Structure:Graph

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Description

Dijkstra algorithm

Demo Code

package com.company.algs.graph.dijkstra;

import java.util.*;

public class Dijkstra {
    private static class Edge {
        private Vertex to;
        private int weight;

        Edge(Vertex to, int weight) {
            this.to = to;
            this.weight = weight;
        }//www  .  j a  v  a 2  s.  c o  m
    }

    private static class Vertex {
        static final int INFINITE = Integer.MAX_VALUE;




        private List<Edge> outEdges;
        private String name;
        private Vertex bestParent;
        private int mark = INFINITE;
        private boolean visited;

        Vertex(String name) {
            this.name = name;
        }

        @Override
        public String toString() {
            return "Vertex{" + "name='" + name + '\'' + ", visited="
                    + visited + '}';
        }
    }

    private void execute(Set<Vertex> vertices) {
        Comparator<Vertex> comparator = new Comparator<Vertex>() {
            @Override
            public int compare(Vertex o1, Vertex o2) {
                return o1.mark < o2.mark ? -1 : (o1.mark > o2.mark ? 1 : 0);
            }
        };

        while (!vertices.isEmpty()) {
            Vertex vertex = Collections.min(vertices, comparator);
            for (Edge edge : vertex.outEdges) {
                if (!edge.to.visited
                        && vertex.mark + edge.weight < edge.to.mark) {
                    edge.to.mark = vertex.mark + edge.weight;
                    edge.to.bestParent = vertex;
                }
            }
            vertices.remove(vertex);
            vertex.visited = true;
        }
    }

    public static void main(String[] args) {
        Vertex vertexA = new Vertex("A");
        Vertex vertexB = new Vertex("B");
        Vertex vertexC = new Vertex("C");
        Vertex vertexD = new Vertex("D");
        Vertex vertexE = new Vertex("E");

        vertexA.outEdges = Arrays.asList(new Edge(vertexB, 1), new Edge(
                vertexC, 2), new Edge(vertexE, 44));

        vertexB.outEdges = Collections.singletonList(new Edge(vertexD, 4));
        vertexC.outEdges = Collections.singletonList(new Edge(vertexE, 23));
        vertexD.outEdges = Collections.singletonList(new Edge(vertexE, 5));
        vertexE.outEdges = Collections.emptyList();

        vertexC.mark = 0; // start vertex
        Dijkstra dijkstra = new Dijkstra();
        dijkstra.execute(new HashSet<>(Arrays.asList(vertexA, vertexB,
                vertexC, vertexD, vertexE)));

        StringBuilder pathBuilder = new StringBuilder();
        Vertex vertex = vertexE;
        while (vertex != null) {
            pathBuilder.insert(0, "[" + vertex.name + "]");
            vertex = vertex.bestParent;
        }

        System.out.println("Best way from vertex C to vertex E: \n"
                + pathBuilder);
    }
}

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