added

Author: vickygit-commits

src/main/java/com/thealgorithms/graph/StronglyConnectedComponentOptimized.java

@@ -15,9 +15,14 @@ public class StronglyConnectedComponentOptimized {
 
     public void btrack(HashMap<Integer, List<Integer>> adjList, int[] visited, Stack<Integer> dfsCallsNodes, int currentNode) {
         visited[currentNode] = 1;
-        for (int neighbor : adjList.get(currentNode)) {
-            if (visited[neighbor] == -1) {
-                btrack(adjList, visited, dfsCallsNodes, neighbor);
+        List<Integer> neighbors = adjList.get(currentNode);
+        
+        // Check for null before iterating
+        if (neighbors != null) {
+            for (int neighbor : neighbors) {
+                if (visited[neighbor] == -1) {
+                    btrack(adjList, visited, dfsCallsNodes, neighbor);
+                }
             }
         }
         dfsCallsNodes.add(currentNode);
@@ -26,9 +31,14 @@ public void btrack(HashMap<Integer, List<Integer>> adjList, int[] visited, Stack
     public void btrack2(HashMap<Integer, List<Integer>> adjRevList, int[] visited, int currentNode, List<Integer> newScc) {
         visited[currentNode] = 1;
         newScc.add(currentNode);
-        for (int neighbor : adjRevList.get(currentNode)) {
-            if (visited[neighbor] == -1) {
-                btrack2(adjRevList, visited, neighbor, newScc);
+        List<Integer> neighbors = adjRevList.get(currentNode);
+        
+        // Check for null before iterating
+        if (neighbors != null) {
+            for (int neighbor : neighbors) {
+                if (visited[neighbor] == -1) {
+                    btrack2(adjRevList, visited, neighbor, newScc);
+                }
             }
         }
     }
@@ -50,8 +60,12 @@ public int getOutput(HashMap<Integer, List<Integer>> adjList, int n) {
         }
 
         for (int i = 0; i < n; i++) {
-            for (int neighbor : adjList.get(i)) {
-                adjRevList.get(neighbor).add(i);
+            List<Integer> neighbors = adjList.get(i);
+            // Check for null before iterating
+            if (neighbors != null) {
+                for (int neighbor : neighbors) {
+                    adjRevList.get(neighbor).add(i);
+                }
             }
         }
 
@@ -69,5 +83,4 @@ public int getOutput(HashMap<Integer, List<Integer>> adjList, int n) {
 
         return stronglyConnectedComponents;
     }
-
 }

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

@@ -1,10 +1,10 @@
-import org.junit.jupiter.api.BeforeEach;
-import org.junit.jupiter.api.Test;
-
 import java.util.ArrayList;
 import java.util.HashMap;
 import java.util.List;
 
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
 import static org.junit.jupiter.api.Assertions.assertEquals;
 
 public class StronglyConnectedComponentOptimizedTest {
@@ -17,7 +17,7 @@ public void setUp() {
     }
 
     @Test
-    public void testSingleComponent() {  
+    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)));
@@ -31,7 +31,7 @@ public void testSingleComponent() {
     }
 
     @Test
-    public void testTwoComponents() {  
+    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)));
@@ -46,7 +46,7 @@ public void testTwoComponents() {
     }
 
     @Test
-    public void testDisconnectedGraph() { 
+    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<>());
@@ -61,7 +61,7 @@ public void testDisconnectedGraph() {
     }
 
     @Test
-    public void testComplexGraph() {  
+    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)));