Create CycleDetectionPrt.java

JAVA/CycleDetectionPrt.java

@@ -0,0 +1,59 @@
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+public class CycleDetectionPrt {
+
+    public static void main(String[] args) {
+
+        Map<Integer, List<Integer>> graph = new HashMap<>();
+        graph.put(0, List.of(1, 2));
+        graph.put(1, List.of(2));
+        graph.put(2, List.of(0, 3));
+        graph.put(3, List.of(3));
+
+        if (containsCycle(graph)) {
+            System.out.println("The graph contains a cycle.");
+        } else {
+            System.out.println("The graph does not contain a cycle.");
+        }
+    }
+
+    public static boolean containsCycle(Map<Integer, List<Integer>> graph) {
+        //track of visited vertices during DFS
+        boolean[] visited = new boolean[graph.size()];
+        // track of vertices in the current DFS traversal
+        boolean[] currentlyInStack = new boolean[graph.size()];
+
+        for (int vertex : graph.keySet()) {
+            if (!visited[vertex] && isCyclic(graph, vertex, visited, currentlyInStack)) {
+                return true;
+            }
+        }
+
+        return false;
+    }
+
+    private static boolean isCyclic(Map<Integer, List<Integer>> graph, int vertex,
+                                    boolean[] visited, boolean[] currentlyInStack) {
+        visited[vertex] = true;
+        currentlyInStack[vertex] = true;
+
+        if (graph.containsKey(vertex)) {
+            for (int neighbor : graph.get(vertex)) {
+                if (!visited[neighbor]) {
+                    if (isCyclic(graph, neighbor, visited, currentlyInStack)) {
+                        return true;
+                    }
+                } else if (currentlyInStack[neighbor]) {
+                    return true; //Cycle detected
+                }
+            }
+        }
+
+        currentlyInStack[vertex] = false; //Backtrack
+
+        return false;
+    }
+}