Visualizing Dijkstra's Algorithm in Java

From Theory to Interactive Graphics

Dijkstra's algorithm is fundamental to computer science, yet it's often taught abstractly. Let's build an interactive visualizer that makes the algorithm tangible.

The Algorithm in Brief

Dijkstra's finds the shortest path from a source node to all other nodes in a weighted graph:

1. Initialize distances (source = 0, others = ∞)
2. Pick unvisited node with smallest distance
3. Update neighbors' distances if shorter path found
4. Mark node as visited
5. Repeat until all nodes visited

Java Implementation

public class Dijkstra {
    private PriorityQueue<Node> queue;
    private Map<Node, Integer> distances;
    private Map<Node, Node> previous;
    
    public void findShortestPath(Graph graph, Node source) {
        initialize(graph, source);
        
        while (!queue.isEmpty()) {
            Node current = queue.poll();
            
            for (Edge edge : current.getEdges()) {
                Node neighbor = edge.getDestination();
                int newDist = distances.get(current) + edge.getWeight();
                
                if (newDist < distances.get(neighbor)) {
                    distances.put(neighbor, newDist);
                    previous.put(neighbor, current);
                    queue.add(neighbor); // Re-add with new priority
                }
            }
        }
    }
}

The Visualization

Using Java Swing, we create an animated visualization:

• Nodes change color as they're processed
• Edges highlight when relaxed
• Distance labels update in real-time
• Step-by-step playback controls

Full source code with Java Swing GUI available on GitHub.