Final Dijkstra fix

desktop.ini

@@ -0,0 +1,2 @@
+[.ShellClassInfo]
+LocalizedResourceName=@dijkstra-priority-queue,0

src/main/java/com/thealgorithms/datastructures/crdt/ORSet.java

@@ -166,7 +166,6 @@ public void merge(ORSet<T> other) {
      */
     public static class Pair<T> {
         private final T element;
-        private final String uniqueTag;
 
         /**
          * Constructs a pair with the specified element and unique tag.
@@ -176,7 +175,6 @@ public static class Pair<T> {
          */
         public Pair(T element, String uniqueTag) {
             this.element = element;
-            this.uniqueTag = uniqueTag;
         }
 
         /**

src/main/java/com/thealgorithms/datastructures/lists/CircleLinkedList.java

@@ -10,7 +10,6 @@
  *
  * @param <E> the type of elements held in this list
  */
-@SuppressWarnings("rawtypes")
 public class CircleLinkedList<E> {
 
     /**

src/main/java/com/thealgorithms/datastructures/lists/SkipList.java

@@ -227,7 +227,6 @@ private static class Node<E> {
         private final List<Node<E>> forward;
         private final List<Node<E>> backward;
 
-        @SuppressWarnings("unchecked")
         Node(E value, int height) {
             this.value = value;
             this.height = height;

src/main/java/com/thealgorithms/datastructures/stacks/StackArray.java

@@ -22,7 +22,6 @@ public class StackArray<T> implements Stack<T> {
     /**
      * Creates a stack with a default capacity.
      */
-    @SuppressWarnings("unchecked")
     public StackArray() {
         this(DEFAULT_CAPACITY);
     }

src/main/java/com/thealgorithms/graphs/DijkstraPriorityQueue.java

@@ -0,0 +1,93 @@
+package com.thealgorithms.graphs;
+
+import java.util.Arrays;
+import java.util.Comparator;
+import java.util.List;
+import java.util.Map;
+import java.util.PriorityQueue;
+
+/**
+ * Dijkstra's algorithm finds the shortest path from a source vertex to all other vertices
+ * in a weighted graph. This implementation uses a PriorityQueue for optimal performance.
+ *
+ * Applications: GPS routing (Google Maps), Network routing (OSPF protocol).
+ *
+ * Time Complexity: O((V + E) log V)
+ * Space Complexity: O(V)
+ */
+public class DijkstraPriorityQueue {
+
+    public static class Edge {
+        int target;
+        int weight;
+
+        public Edge(int target, int weight) {
+            this.target = target;
+            this.weight = weight;
+        }
+    }
+
+    /**
+     * Finds the shortest paths from the source to all other vertices.
+     *
+     * @param source the starting vertex
+     * @param graph the adjacency list representation of the graph
+     * @param numVertices total number of vertices in the graph
+     * @return an array of shortest distances from source
+     * @throws IllegalArgumentException if any edge weight is negative or input is invalid
+     */
+    public int[] runDijkstra(int source, Map<Integer, List<Edge>> graph, int numVertices) {
+        // Validation for number of vertices
+        if (numVertices <= 0) {
+            return new int[0];
+        }
+
+        // Validation for null graph or invalid source index
+        if (graph == null || source < 0 || source >= numVertices) {
+            int[] emptyDist = new int[numVertices];
+            Arrays.fill(emptyDist, Integer.MAX_VALUE);
+            if (source >= 0 && source < numVertices) {
+                emptyDist[source] = 0;
+            }
+            return emptyDist;
+        }
+
+        // Min-priority queue based on distance (int[1])
+        PriorityQueue<int[]> pq = new PriorityQueue<>(Comparator.comparingInt(a -> a[1]));
+        int[] dist = new int[numVertices];
+        Arrays.fill(dist, Integer.MAX_VALUE);
+
+        dist[source] = 0;
+        pq.add(new int[] {source, 0});
+
+        while (!pq.isEmpty()) {
+            int[] current = pq.poll();
+            int u = current[0];
+            int d = current[1];
+
+            // If current distance is already greater than stored distance, skip
+            // This is a common "Partial" coverage point if not tested with multiple paths
+            if (d > dist[u]) {
+                continue;
+            }
+
+            List<Edge> neighbors = graph.get(u);
+            if (neighbors == null) {
+                continue;
+            }
+
+            for (Edge edge : neighbors) {
+                // Dijkstra's algorithm does not support negative weights
+                if (edge.weight < 0) {
+                    throw new IllegalArgumentException("Graph contains negative weight edge: " + edge.weight);
+                }
+
+                if (dist[u] != Integer.MAX_VALUE && dist[u] + edge.weight < dist[edge.target]) {
+                    dist[edge.target] = dist[u] + edge.weight;
+                    pq.add(new int[] {edge.target, dist[edge.target]});
+                }
+            }
+        }
+        return dist;
+    }
+}

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

@@ -1,9 +1,10 @@
 package com.thealgorithms.others;
 
+import java.util.Comparator;
 import java.util.HashMap;
 import java.util.Map;
-import java.util.NavigableSet;
-import java.util.TreeSet;
+import java.util.PriorityQueue;
+
 /**
  * Dijkstra's algorithm,is a graph search algorithm that solves the
  * single-source shortest path problem for a graph with nonnegative edge path
@@ -12,7 +13,10 @@
  * <p>
  * NOTE: The inputs to Dijkstra's algorithm are a directed and weighted graph
  * consisting of 2 or more nodes, generally represented by an adjacency matrix
- * or list, and a start node.
+ * or list, and a start node. This implementation uses a binary heap
+ * (Java's {@link PriorityQueue}) to achieve a time complexity of
+ * O((V + E) log V) in practice. Practical use-cases include GPS routing and
+ * network routing where all edge weights are non-negative.
  *
  * <p>
  * Original source of code:
@@ -182,46 +186,72 @@ public void dijkstra(String startName) {
             return;
         }
         final Vertex source = graph.get(startName);
-        NavigableSet<Vertex> q = new TreeSet<>();
 
-        // set-up vertices
+        // initialize distances
         for (Vertex v : graph.values()) {
             v.previous = v == source ? source : null;
             v.dist = v == source ? 0 : Integer.MAX_VALUE;
-            q.add(v);
         }
 
-        dijkstra(q);
-    }
+        // Priority queue of (vertex, knownDist) entries. We push new entries when
+        // a shorter distance is found; stale entries are ignored when polled.
+        PriorityQueue<NodeEntry> pq = new PriorityQueue<>(Comparator
+                .comparingInt((NodeEntry e) -> e.dist)
+                .thenComparing(e -> e.vertex.name));
+
+        pq.add(new NodeEntry(source, 0));
 
+        dijkstra(pq);
+    }
     /**
-     * Implementation of dijkstra's algorithm using a binary heap.
+     * Implementation of dijkstra's algorithm using a priority queue of entries.
      */
-    private void dijkstra(final NavigableSet<Vertex> q) {
-        Vertex u;
-        Vertex v;
-        while (!q.isEmpty()) {
-            // vertex with shortest distance (first iteration will return source)
-            u = q.pollFirst();
+    private void dijkstra(final PriorityQueue<NodeEntry> pq) {
+        while (!pq.isEmpty()) {
+            final NodeEntry entry = pq.poll();
+            final Vertex u = entry.vertex;
+
+            // ignore stale/popped entries
+            if (entry.dist != u.dist) {
+                continue;
+            }
+
             if (u.dist == Integer.MAX_VALUE) {
-                break; // we can ignore u (and any other remaining vertices) since they are
-                       // unreachable
+                break; // remaining vertices are unreachable
             }
+
             // look at distances to each neighbour
             for (Map.Entry<Vertex, Integer> a : u.neighbours.entrySet()) {
-                v = a.getKey(); // the neighbour in this iteration
+                final Vertex v = a.getKey(); // the neighbour in this iteration
+                final int weight = a.getValue();
 
-                final int alternateDist = u.dist + a.getValue();
+                if (weight < 0) {
+                    throw new IllegalArgumentException("Graph contains negative edge weight: " + weight);
+                }
+
+                final int alternateDist = u.dist + weight;
                 if (alternateDist < v.dist) { // shorter path to neighbour found
-                    q.remove(v);
                     v.dist = alternateDist;
                     v.previous = u;
-                    q.add(v);
+                    pq.add(new NodeEntry(v, alternateDist));
                 }
             }
         }
     }
 
+    /**
+     * Helper entry for the priority queue to avoid costly removals (no decrease-key).
+     */
+    private static class NodeEntry {
+        final Vertex vertex;
+        final int dist;
+
+        NodeEntry(Vertex vertex, int dist) {
+            this.vertex = vertex;
+            this.dist = dist;
+        }
+    }
+
     /**
      * Prints a path from the source to the specified vertex
      */

src/main/java/com/thealgorithms/physics/DampedOscillator.java

@@ -34,10 +34,6 @@ public final class DampedOscillator {
     /** Damping coefficient (s⁻¹). */
     private final double gamma;
 
-    private DampedOscillator() {
-        throw new AssertionError("No instances.");
-    }
-
     /**
      * Constructs a damped oscillator model.
      *

src/main/java/com/thealgorithms/physics/SimplePendulumRK4.java

@@ -8,10 +8,6 @@
  */
 public final class SimplePendulumRK4 {
 
-    private SimplePendulumRK4() {
-        throw new AssertionError("No instances.");
-    }
-
     private final double length; // meters
     private final double g; // acceleration due to gravity (m/s^2)
 

src/main/java/com/thealgorithms/scheduling/EDFScheduling.java

@@ -10,8 +10,6 @@
  * This scheduling algorithm is ideal for real-time systems where meeting deadlines is critical.
  */
 public final class EDFScheduling {
-    private EDFScheduling() {
-    }
 
     private List<Process> processes;
 

src/main/java/com/thealgorithms/scheduling/HighestResponseRatioNextScheduling.java

@@ -30,14 +30,12 @@ private HighestResponseRatioNextScheduling() {
      * Represents a process in the scheduling algorithm.
      */
     private static class Process {
-        String name;
         int arrivalTime;
         int burstTime;
         int turnAroundTime;
         boolean finished;
 
         Process(String name, int arrivalTime, int burstTime) {
-            this.name = name;
             this.arrivalTime = arrivalTime;
             this.burstTime = burstTime;
             this.turnAroundTime = 0;

src/main/java/com/thealgorithms/scheduling/LotteryScheduling.java

@@ -11,8 +11,6 @@
  * Processes with more tickets have a higher chance of being selected.
  */
 public final class LotteryScheduling {
-    private LotteryScheduling() {
-    }
 
     private List<Process> processes;
     private Random random;

src/main/java/com/thealgorithms/searches/PerfectBinarySearch.java

@@ -19,11 +19,11 @@ public class PerfectBinarySearch<T> implements SearchAlgorithm {
     /**
      * @param array is an array where the element should be found
      * @param key is an element which should be found
-     * @param <T> is any comparable type
+     * @param <U> is any comparable type
      * @return index of the element
      */
     @Override
-    public <T extends Comparable<T>> int find(T[] array, T key) {
+    public <U extends Comparable<U>> int find(U[] array, U key) {
         return search(array, key, 0, array.length - 1);
     }
 

src/main/java/com/thealgorithms/sorts/AdaptiveMergeSort.java

@@ -1,7 +1,6 @@
 package com.thealgorithms.sorts;
 
 public class AdaptiveMergeSort implements SortAlgorithm {
-    @SuppressWarnings("unchecked")
     public <T extends Comparable<T>> T[] sort(T[] array) {
         if (array.length <= 1) {
             return array;

src/main/java/com/thealgorithms/sorts/SpreadSort.java

@@ -266,7 +266,6 @@ int size() {
          *
          * @return an array containing all elements in the bucket
          */
-        @SuppressWarnings("unchecked")
         T[] toArray() {
             return Arrays.copyOf(elements, size);
         }

src/test/java/com/thealgorithms/datastructures/bag/BagTest.java

@@ -99,7 +99,7 @@ void testIterator() {
     void testIteratorEmptyBag() {
         Bag<String> bag = new Bag<>();
         int count = 0;
-        for (String ignored : bag) {
+        for (String item : bag) {
             org.junit.jupiter.api.Assertions.fail("Iterator should not return any items for an empty bag");
         }
         assertEquals(0, count, "Iterator should not traverse any items in an empty bag");