Add StronglyConnectedComponentOptimized (#5825)

src/test/java/com/thealgorithms/graph/StronglyConnectedComponentOptimizedTest.java

@@ -0,0 +1,78 @@
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+public class StronglyConnectedComponentOptimizedTest {
+
+    private StronglyConnectedComponentOptimized sccOptimized;
+
+    @BeforeEach
+    public void setUp() {
+        sccOptimized = new StronglyConnectedComponentOptimized();
+    }
+
+    @Test
+    public void testSingleComponent() {
+        // Create a simple graph with 3 nodes, all forming one SCC
+        HashMap<Integer, List<Integer>> adjList = new HashMap<>();
+        adjList.put(0, new ArrayList<>(List.of(1)));
+        adjList.put(1, new ArrayList<>(List.of(2)));
+        adjList.put(2, new ArrayList<>(List.of(0)));
+
+        int result = sccOptimized.getOutput(adjList, 3);
+
+        // The entire graph is one strongly connected component
+        assertEquals(1, result, "There should be 1 strongly connected component.");
+    }
+
+    @Test
+    public void testTwoComponents() {
+        // Create a graph with 4 nodes and two SCCs: {0, 1, 2} and {3}
+        HashMap<Integer, List<Integer>> adjList = new HashMap<>();
+        adjList.put(0, new ArrayList<>(List.of(1)));
+        adjList.put(1, new ArrayList<>(List.of(2)));
+        adjList.put(2, new ArrayList<>(List.of(0)));
+        adjList.put(3, new ArrayList<>());
+
+        int result = sccOptimized.getOutput(adjList, 4);
+
+        // There are 2 SCCs: {0, 1, 2} and {3}
+        assertEquals(2, result, "There should be 2 strongly connected components.");
+    }
+
+    @Test
+    public void testDisconnectedGraph() {
+        // Create a graph with 4 nodes that are all disconnected
+        HashMap<Integer, List<Integer>> adjList = new HashMap<>();
+        adjList.put(0, new ArrayList<>());
+        adjList.put(1, new ArrayList<>());
+        adjList.put(2, new ArrayList<>());
+        adjList.put(3, new ArrayList<>());
+
+        int result = sccOptimized.getOutput(adjList, 4);
+
+        // Each node is its own strongly connected component
+        assertEquals(4, result, "There should be 4 strongly connected components.");
+    }
+
+    @Test
+    public void testComplexGraph() {
+        // Create a more complex graph with multiple SCCs
+        HashMap<Integer, List<Integer>> adjList = new HashMap<>();
+        adjList.put(0, new ArrayList<>(List.of(1)));
+        adjList.put(1, new ArrayList<>(List.of(2)));
+        adjList.put(2, new ArrayList<>(List.of(0, 3)));
+        adjList.put(3, new ArrayList<>(List.of(4)));
+        adjList.put(4, new ArrayList<>(List.of(5)));
+        adjList.put(5, new ArrayList<>(List.of(3)));
+
+        int result = sccOptimized.getOutput(adjList, 6);
+
+        // There are 2 SCCs: {0, 1, 2} and {3, 4, 5}
+        assertEquals(2, result, "There should be 2 strongly connected components.");
+    }
+}