Merge pull request #70 from gandharva-gk/main

Djikstra Algorithm in Java

Author: jvm-coder

djikstra.java

@@ -0,0 +1,164 @@
+import java.util.Scanner;
+import java.util.Arrays;
+
+class Node{
+    int val;
+    int weight;
+    Node next;
+
+    public Node(int val,int weight){
+        this.val = val;
+        this.weight = weight;
+        this.next = null;
+    }
+}
+
+class Graph{
+
+    public Node[] CreateGraph(int n){
+        Node[] Graph = new Node[n];
+        return Graph;
+    }
+
+    /* This Function adds Edge between the Source and Destination */
+
+    public void AddEdge(Node[] Graph,int src,int dest,int weight){
+
+
+        if(Graph[src] == null){
+
+            Graph[src] = new Node(dest,weight);
+            return;
+
+        }
+
+        else{
+
+            Node temp = new Node(dest,weight);
+
+            temp.next = Graph[src];
+
+            Graph[src] = temp;
+
+        }
+
+    }
+
+    /* This Function returns the Index of the Node that has the Least Shortest Distance and is UnVisited. */
+
+    public int MinIndex(int[] dist,boolean[] visited){
+        int min = Integer.MAX_VALUE;
+        int min_index = -1;
+
+        for(int i = 0;i<dist.length;i++){
+
+            if(!visited[i] && min > dist[i]){
+                min = dist[i];
+                min_index = i;
+            }
+        }
+
+        return min_index;
+    }
+
+}
+
+
+public class djikstra {
+    public static void main(String[] args) {
+        
+        Scanner scan = new Scanner(System.in);
+
+        Graph g = new Graph();
+
+
+        System.out.print("Enter the Number of Nodes in the Graph : ");
+
+        int num = scan.nextInt();
+
+        Node[] Graph = g.CreateGraph(num);
+
+        System.out.print("Enter the Total Number of Edges in the Graph : ");
+
+        int edges = scan.nextInt();
+
+        System.out.println("Now Enter all the Edges as Source Destination Weight");
+
+        /* Storing the edges */
+
+        for(int i = 0;i<edges;i++){
+            int src = scan.nextInt();
+            int dest = scan.nextInt();
+            int weight = scan.nextInt();
+
+            g.AddEdge(Graph, src, dest, weight);
+            g.AddEdge(Graph, dest, src, weight);
+
+        }
+
+        System.out.print("Enter the Node from where you want to find the Shortest Distance to all the other Nodes : ");
+
+        int start = scan.nextInt();
+
+        /* Distance Array Which Stores the Shortest Distance from the Given Node to all other Nodes */
+
+        int[] dist = new int[num];
+
+        /* Boolean Array which stores whether a Node is Visited or Not */
+
+        boolean[] visited = new boolean[num];
+
+        /* Initialize all the Distances to MAX Values. */
+
+        Arrays.fill(dist, Integer.MAX_VALUE);
+
+        /* Initialize the Shortest Distance to reach the Start Node to 0 */
+
+        dist[start] = 0;
+
+        while(true){
+
+            /* At Every Iteration Find the Node that has the least Shortest Distance Value and is Unvisited. */
+
+            int min_index = g.MinIndex(dist, visited);
+
+            /* If you haven't found any Node that has Shortest Distance and Unvisted then exit the loop */
+
+            if(min_index == -1){
+                break;
+            }
+
+            /* Mark the Node as Visited. */
+
+            visited[min_index] = true;
+
+            Node temp = Graph[min_index];
+
+            /* Now Iterate over all it's Neighbours and update the values if the 
+            (Shortest Distance to this Node) + (Edge Weight between this Node and Neighouring Node) 
+            is less than the Shortest Distance to the neighbour in Distance Array  */
+
+            while(temp != null){
+
+                if(dist[temp.val] > dist[min_index] + temp.weight && !visited[temp.val]){
+                    dist[temp.val] = dist[min_index] + temp.weight;
+                }
+
+                temp = temp.next;
+
+            }
+        }
+
+        /* Printing the Shortest Distances from the Start Node to all the other Nodes */
+
+        for(int i = 0;i<num;i++){
+            System.out.print(dist[i] + " ");
+        }
+
+        System.out.println("");
+
+
+        scan.close();
+
+    }
+}