Create Dijkstra.java with implementation of Dijkstra's Algorithm in J…

…ava, featuring a priority queue for shortest path determination and a HashMap for the adjacency list

Algorithms/DijkstraAlgorithm/Dijkstra.java

@@ -0,0 +1,62 @@
+import java.util.*;
+
+class Graph {
+    private Map<Integer, List<Pair>> adjList = new HashMap<>();
+
+    private static class Pair {
+        int vertex;
+        int weight;
+        Pair(int vertex, int weight) {
+            this.vertex = vertex;
+            this.weight = weight;
+        }
+    }
+
+    public void addEdge(int u, int v, int weight) {
+        adjList.putIfAbsent(u, new ArrayList<>());
+        adjList.get(u).add(new Pair(v, weight));
+        adjList.putIfAbsent(v, new ArrayList<>());
+        adjList.get(v).add(new Pair(u, weight)); // For undirected graph
+    }
+
+    public Map<Integer, Integer> dijkstra(int start) {
+        PriorityQueue<Pair> queue = new PriorityQueue<>(Comparator.comparingInt(a -> a.weight));
+        Map<Integer, Integer> distances = new HashMap<>();
+        for (int vertex : adjList.keySet()) {
+            distances.put(vertex, Integer.MAX_VALUE);
+        }
+        distances.put(start, 0);
+        queue.add(new Pair(start, 0));
+
+        while (!queue.isEmpty()) {
+            Pair current = queue.poll();
+            for (Pair neighbor : adjList.getOrDefault(current.vertex, new ArrayList<>())) {
+                int newDist = distances.get(current.vertex) + neighbor.weight;
+                if (newDist < distances.get(neighbor.vertex)) {
+                    distances.put(neighbor.vertex, newDist);
+                    queue.add(new Pair(neighbor.vertex, newDist));
+                }
+            }
+        }
+        return distances;
+    }
+
+    // Example usage
+    public static void main(String[] args) {
+        Graph g = new Graph();
+        g.addEdge(0, 1, 10);
+        g.addEdge(0, 2, 5);
+        g.addEdge(1, 2, 2);
+        g.addEdge(1, 3, 1);
+        g.addEdge(2, 1, 3);
+        g.addEdge(2, 3, 9);
+        g.addEdge(2, 4, 2);
+        g.addEdge(3, 4, 6);
+        g.addEdge(4, 3, 4);
+
+        Map<Integer, Integer> distances = g.dijkstra(0);
+        for (Map.Entry<Integer, Integer> entry : distances.entrySet()) {
+            System.out.println("Distance from 0 to " + entry.getKey() + " is " + entry.getValue());
+        }
+    }
+}