Added Dijkstra's Algorithm in Greedy Algorithms

Author: Farai Mugaviri

src/main/java/com/thealgorithms/greedyalgorithms/Dijkstra.java

@@ -0,0 +1,71 @@
+package com.thealgorithms.greedyalgorithms;
+
+import java.util.*;
+
+/**
+ * Dijkstra's shortest path algorithm for non-negative weighted graphs.
+ *
+ * Provides a method to compute shortest distances from a source node to all
+ * other nodes using an adjacency list representation.
+ */
+public final class Dijkstra {
+    private Dijkstra() {}
+
+    /**
+     * Compute shortest distances from source to all vertices.
+     *
+     * @param n number of vertices (vertices are 0..n-1)
+     * @param adj adjacency list where adj[u] is a list of (v, weight) pairs
+     * @param src source vertex
+     * @return array of distances where dist[i] is shortest distance or Long.MAX_VALUE if unreachable
+     */
+    public static long[] shortestPaths(int n, List<List<Edge>> adj, int src) {
+        long[] dist = new long[n];
+        Arrays.fill(dist, Long.MAX_VALUE);
+        dist[src] = 0L;
+
+        PriorityQueue<Node> pq = new PriorityQueue<>(Comparator.comparingLong(a -> a.dist));
+        pq.add(new Node(src, 0L));
+
+        boolean[] visited = new boolean[n];
+
+        while (!pq.isEmpty()) {
+            Node cur = pq.poll();
+            int u = cur.id;
+            if (visited[u]) continue;
+            visited[u] = true;
+
+            for (Edge e : adj.get(u)) {
+                int v = e.to;
+                long w = e.weight;
+                if (dist[u] != Long.MAX_VALUE && dist[u] + w < dist[v]) {
+                    dist[v] = dist[u] + w;
+                    pq.add(new Node(v, dist[v]));
+                }
+            }
+        }
+
+        return dist;
+    }
+
+    /** Simple edge class for adjacency lists */
+    public static class Edge {
+        public final int to;
+        public final long weight;
+
+        public Edge(int to, long weight) {
+            this.to = to;
+            this.weight = weight;
+        }
+    }
+
+    private static class Node {
+        final int id;
+        final long dist;
+
+        Node(int id, long dist) {
+            this.id = id;
+            this.dist = dist;
+        }
+    }
+}