Add PR2.java

Miscellaneous/PR2.java

@@ -0,0 +1,59 @@
+import java.util.*;
+
+public class PR2 {
+
+    public static boolean detectCycle(int[][] edgeList) {
+        if (edgeList.length == 0) {
+            return false;
+        }
+
+        Map<Integer, Set<Integer>> graph = new HashMap<>();
+        int[] inorder = new int[edgeList.length];
+
+        for (int[] edge : edgeList) {
+            graph.putIfAbsent(edge[0], new HashSet<>());
+            graph.get(edge[0]).add(edge[1]);
+
+            inorder[edge[1]]++;
+        }
+
+        Queue<Integer> q = new LinkedList<>();
+
+        for (int i = 0; i < inorder.length; i++) {
+            if (inorder[i] == 0) {
+                q.offer(i);
+            }
+        }
+
+        int nodeCount = 0;
+
+        while (!q.isEmpty()) {
+            int key = q.poll();
+            ++nodeCount;
+
+            if (!graph.containsKey(key)) {
+                continue;
+            }
+
+            for (int neighbour : graph.get(key)) {
+                inorder[neighbour]--;
+
+                if (inorder[neighbour] == 0) {
+                    q.offer(neighbour);
+                }
+            }
+        }
+
+        return edgeList.length - nodeCount > 1;
+    }
+
+    public static void main(String[] args) {
+        int[][] edgeList1 = new int[][] { { 0, 1 }, { 1, 3 }, { 2, 3 }, { 1, 2 }, { 4, 1 }, { 0, 4 }, { 1, 3 } };
+        int[][] edgeList2 = new int[][] { { 0, 1 }, { 1, 3 }, { 2, 3 }, { 3, 4 }, { 1, 2 }, { 4, 1 }, { 0, 4 } };
+
+        System.out.println(detectCycle(edgeList1)); // no cycle - return false
+        System.out.println(detectCycle(edgeList2)); // cycle present - return true
+
+        return;
+    }
+}