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Commit 08423dc

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Dijkstra’s Algorithm in Java
1 parent 41229ae commit 08423dc

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‎Graph/Dijkstras/Demo.java

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/*
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Copyright (C) Deepali Srivastava - All Rights Reserved
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This code is part of DSA course available on CourseGalaxy.com
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*/
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package Dijkstras;
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public class Demo
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{
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public static void main(String [] args)
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{
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DirectedWeightedGraph g = new DirectedWeightedGraph();
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g.insertVertex("Zero");
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g.insertVertex("One");
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g.insertVertex("Two");
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g.insertVertex("Three");
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g.insertVertex("Four");
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g.insertVertex("Five");
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g.insertVertex("Six");
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g.insertVertex("Seven");
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g.insertVertex("Eight");
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g.insertEdge("Zero","Three", 2);
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g.insertEdge("Zero","One", 5);
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g.insertEdge("Zero","Four", 8);
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g.insertEdge("One","Four", 2);
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g.insertEdge("Two","One", 3);
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g.insertEdge("Two","Five", 4);
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g.insertEdge("Three","Four", 7);
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g.insertEdge("Three","Six", 8);
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g.insertEdge("Four","Five", 9);
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g.insertEdge("Four","Seven", 4);
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g.insertEdge("Five","One", 6);
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g.insertEdge("Six","Seven", 9);
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g.insertEdge("Seven","Three", 5);
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g.insertEdge("Seven","Five", 3);
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g.insertEdge("Seven","Eight", 5);
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g.insertEdge("Eight","Five", 3);
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g.findPaths("Zero");
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}
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}
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/*
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Copyright (C) Deepali Srivastava - All Rights Reserved
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This code is part of DSA course available on CourseGalaxy.com
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*/
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package Dijkstras;
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public class DirectedWeightedGraph
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{
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public final int MAX_VERTICES = 30;
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int n;
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int e;
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int [][] adj;
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Vertex [] vertexList;
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private static final int TEMPORARY = 1;
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private static final int PERMANENT = 2;
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private static final int NIL = -1;
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private static final int INFINITY = 99999;
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public DirectedWeightedGraph()
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{
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adj = new int [MAX_VERTICES][MAX_VERTICES];
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vertexList = new Vertex[MAX_VERTICES];
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}
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private void dijkstra(int s)
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{
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int v,c;
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for(v=0; v<n; v++)
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{
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vertexList[v].status = TEMPORARY;
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vertexList[v].pathLength = INFINITY;
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vertexList[v].predecessor = NIL;
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}
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vertexList[s].pathLength = 0;
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while(true)
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{
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c=tempVertexMinPL();
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if(c==NIL)
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return;
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vertexList[c].status = PERMANENT;
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for(v=0; v<n; v++)
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{
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if(isAdjacent(c,v) && vertexList[v].status == TEMPORARY)
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if( vertexList[c].pathLength + adj[c][v] < vertexList[v].pathLength )
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{
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vertexList[v].predecessor = c;
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vertexList[v].pathLength = vertexList[c].pathLength + adj[c][v];
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}
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}
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}
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}
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private int tempVertexMinPL( )
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{
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int min=INFINITY;
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int x=NIL;
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for(int v=0; v<n; v++)
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{
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if(vertexList[v].status == TEMPORARY && vertexList[v].pathLength < min)
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{
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min=vertexList[v].pathLength;
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x=v;
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}
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}
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return x;
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}
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public void findPaths(String source)
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{
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int s = getIndex(source);
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dijkstra(s);
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System.out.println("Source Vertex : " + source + "\n");
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for(int v=0; v<n; v++)
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{
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System.out.println("Destination Vertex : " + vertexList[v]);
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if( vertexList[v].pathLength == INFINITY )
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System.out.println("There is no path from " + source + " to vertex " + vertexList[v] + "\n");
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else
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findPath(s,v);
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}
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}
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private void findPath(int s, int v)
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{
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int i,u;
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int [] path = new int[n];
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int sd=0;
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int count=0;
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while(v!=s)
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{
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count++;
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path[count] = v;
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u = vertexList[v].predecessor;
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sd += adj[u][v];
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v=u;
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}
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count++;
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path[count]=s;
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System.out.print("Shortest Path is : ");
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for(i=count; i>=1; i--)
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System.out.print(path[i] + " ");
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System.out.println("\n Shortest distance is : " + sd + "\n");
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}
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private int getIndex(String s)
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{
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for(int i=0; i<n; i++)
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if(s.equals(vertexList[i].name))
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return i;
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throw new RuntimeException("Invalid Vertex");
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}
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public void insertVertex(String name)
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{
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vertexList[n++] = new Vertex(name);
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}
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private boolean isAdjacent(int u, int v)
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{
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return (adj[u][v]!=0);
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}
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/*Insert an edge (s1,s2) */
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public void insertEdge(String s1, String s2, int wt)
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{
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int u = getIndex(s1);
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int v = getIndex(s2);
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if(u==v)
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throw new IllegalArgumentException("Not a valid edge");
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if(adj[u][v] !=0 )
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System.out.print("Edge already present");
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else
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{
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adj[u][v]=wt;
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e++;
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}
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}
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}
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‎Graph/Dijkstras/Vertex.java

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/*
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Copyright (C) Deepali Srivastava - All Rights Reserved
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This code is part of DSA course available on CourseGalaxy.com
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*/
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package Dijkstras;
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public class Vertex
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{
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String name;
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int status;
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int predecessor;
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int pathLength;
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Vertex(String name)
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{
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this.name = name;
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}
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public String toString()
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{
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return name;
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}
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}

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