djikstra algorithm code example

Example 1: java djikstra's algorithm

import java.util.*; 
public class DPQ { 
    private int dist[]; 
    private Set<Integer> settled; 
    private PriorityQueue<Node> pq; 
    private int V; // Number of vertices 
    List<List<Node> > adj; 
  
    public DPQ(int V) 
    { 
        this.V = V; 
        dist = new int[V]; 
        settled = new HashSet<Integer>(); 
        pq = new PriorityQueue<Node>(V, new Node()); 
    } 
  
    // Function for Dijkstra's Algorithm 
    public void dijkstra(List<List<Node> > adj, int src) 
    { 
        this.adj = adj; 
  
        for (int i = 0; i < V; i++) 
            dist[i] = Integer.MAX_VALUE; 
  
        // Add source node to the priority queue 
        pq.add(new Node(src, 0)); 
  
        // Distance to the source is 0 
        dist[src] = 0; 
        while (settled.size() != V) { 
  
            // remove the minimum distance node  
            // from the priority queue  
            int u = pq.remove().node; 
  
            // adding the node whose distance is 
            // finalized 
            settled.add(u); 
  
            e_Neighbours(u); 
        } 
    } 
  
    // Function to process all the neighbours  
    // of the passed node 
    private void e_Neighbours(int u) 
    { 
        int edgeDistance = -1; 
        int newDistance = -1; 
  
        // All the neighbors of v 
        for (int i = 0; i < adj.get(u).size(); i++) { 
            Node v = adj.get(u).get(i); 
  
            // If current node hasn't already been processed 
            if (!settled.contains(v.node)) { 
                edgeDistance = v.cost; 
                newDistance = dist[u] + edgeDistance; 
  
                // If new distance is cheaper in cost 
                if (newDistance < dist[v.node]) 
                    dist[v.node] = newDistance; 
  
                // Add the current node to the queue 
                pq.add(new Node(v.node, dist[v.node])); 
            } 
        } 
    } 
  
    // Driver code 
    public static void main(String arg[]) 
    { 
        int V = 5; 
        int source = 0; 
  
        // Adjacency list representation of the  
        // connected edges 
        List<List<Node> > adj = new ArrayList<List<Node> >(); 
  
        // Initialize list for every node 
        for (int i = 0; i < V; i++) { 
            List<Node> item = new ArrayList<Node>(); 
            adj.add(item); 
        } 
  
        // Inputs for the DPQ graph 
        adj.get(0).add(new Node(1, 9)); 
        adj.get(0).add(new Node(2, 6)); 
        adj.get(0).add(new Node(3, 5)); 
        adj.get(0).add(new Node(4, 3)); 
  
        adj.get(2).add(new Node(1, 2)); 
        adj.get(2).add(new Node(3, 4)); 
  
        // Calculate the single source shortest path 
        DPQ dpq = new DPQ(V); 
        dpq.dijkstra(adj, source); 
  
        // Print the shortest path to all the nodes 
        // from the source node 
        System.out.println("The shorted path from node :"); 
        for (int i = 0; i < dpq.dist.length; i++) 
            System.out.println(source + " to " + i + " is "
                               + dpq.dist[i]); 
    } 
} 
  
// Class to represent a node in the graph 
class Node implements Comparator<Node> { 
    public int node; 
    public int cost; 
  
    public Node() 
    { 
    } 
  
    public Node(int node, int cost) 
    { 
        this.node = node; 
        this.cost = cost; 
    } 
  
    @Override
    public int compare(Node node1, Node node2) 
    { 
        if (node1.cost < node2.cost) 
            return -1; 
        if (node1.cost > node2.cost) 
            return 1; 
        return 0; 
    } 
}

Example 2: dijkstra algorithm c++

#include<bits/stdc++.h>
using namespace std;

int main()
{
	int n = 9;
	
	int mat[9][9] = { { 100,4,100,100,100,100,100,8,100}, 
                      { 4,100,8,100,100,100,100,11,100}, 
                      {100,8,100,7,100,4,100,100,2}, 
                      {100,100,7,100,9,14,100,100,100}, 
                      {100,100,100,9,100,100,100,100,100}, 
                      {100,100,4,14,10,100,2,100,100}, 
                      {100,100,100,100,100,2,100,1,6}, 
                      {8,11,100,100,100,100,1,100,7}, 
                      {100,100,2,100,100,100,6,7,100}};
	
	int src = 0;
	int count = 1;
	
	int path[n];
	for(int i=0;i<n;i++)
		path[i] = mat[src][i];
	
	int visited[n] = {0};
	visited[src] = 1;
	
	while(count<n)
	{
		int minNode;
		int minVal = 100;
		
		for(int i=0;i<n;i++)
			if(visited[i] == 0 && path[i]<minVal)
			{
				minVal = path[i];
				minNode = i;
			}
		
		visited[minNode] = 1;
		
		for(int i=0;i<n;i++)
			if(visited[i] == 0)
				path[i] = min(path[i],minVal+mat[minNode][i]);
					
		count++;
	}
	
	path[src] = 0;
	for(int i=0;i<n;i++)
		cout<<src<<" -> "<<path[i]<<endl;
	
	return(0);
}

Example 3: Dijkstra's Weighted Graph Shortest Path in c++

#include <limits.h> 
#include <stdio.h> 
  

#define V 9 
  

int minDistance(int dist[], bool sptSet[]) 
{ 

    int min = INT_MAX, min_index; 
  
    for (int v = 0; v < V; v++) 
        if (sptSet[v] == false && dist[v] <= min) 
            min = dist[v], min_index = v; 
  
    return min_index; 
} 
  

void printSolution(int dist[]) 
{ 
    printf("Vertex \t\t Distance from Source\n"); 
    for (int i = 0; i < V; i++) 
        printf("%d \t\t %d\n", i, dist[i]); 
} 
  

void dijkstra(int graph[V][V], int src) 
{ 
    int dist[V]; 
    
  
    bool sptSet[V];
 
    for (int i = 0; i < V; i++) 
        dist[i] = INT_MAX, sptSet[i] = false; 
  
  
    dist[src] = 0; 
  
  
    for (int count = 0; count < V - 1; count++) { 
       
        int u = minDistance(dist, sptSet); 
  
       
        sptSet[u] = true; 
  
       
        for (int v = 0; v < V; v++) 
  
           
            if (!sptSet[v] && graph[u][v] && dist[u] != INT_MAX 
                && dist[u] + graph[u][v] < dist[v]) 
                dist[v] = dist[u] + graph[u][v]; 
    } 
  
 
    printSolution(dist); 
} 
  

int main() 
{ 
    
    int graph[V][V] = { { 0, 4, 0, 0, 0, 0, 0, 8, 0 }, 
                        { 4, 0, 8, 0, 0, 0, 0, 11, 0 }, 
                        { 0, 8, 0, 7, 0, 4, 0, 0, 2 }, 
                        { 0, 0, 7, 0, 9, 14, 0, 0, 0 }, 
                        { 0, 0, 0, 9, 0, 10, 0, 0, 0 }, 
                        { 0, 0, 4, 14, 10, 0, 2, 0, 0 }, 
                        { 0, 0, 0, 0, 0, 2, 0, 1, 6 }, 
                        { 8, 11, 0, 0, 0, 0, 1, 0, 7 }, 
                        { 0, 0, 2, 0, 0, 0, 6, 7, 0 } }; 
  
    dijkstra(graph, 0); 
  
    return 0; 
}