add bfs topo sort

Author: joney000

TopologicalOrderBFS.java

@@ -0,0 +1,44 @@
+// Time Complexity : O(N) and Space O(N) Heap space,
+// Advantage over stack approach: handle cycle detection
+
+class Solution {
+    public boolean isCycle(int numCourses, int[][] prerequisites) {
+        if(numCourses <= 1)return true;
+        try{
+            
+            int d[] = new int[numCourses];
+	   				// Graph as Adj List
+						LinkedList<Integer> [] adj = new LinkedList[numCourses];
+	  				for(int vertex = 0; vertex < numCourses; vertex ++){
+							adj[vertex] = new LinkedList<Integer>();
+						}
+
+            for(int[] edge: prerequisites){
+                d[edge[1]]++;
+                adj[edge[0]].add(edge[1]); // directed
+            }
+	   				LinkedList<Integer> queue = new LinkedList<>();
+            for(int vertex = 0; vertex < numCourses; vertex ++){
+							if(d[vertex] == 0){
+								queue.add(vertex);
+							}
+						}
+				    LinkedList<Integer> topologicalOrder = new LinkedList<>();
+				    while(!queue.isEmpty()){
+							int parent = (Integer)queue.removeFirst();
+							topologicalOrder.add(parent);
+							for(int child: adj[parent]){
+								d[child]--;
+								if(d[child] == 0){
+									queue.addLast(child);
+								}
+							}
+						}
+						return topologicalOrder.size() == numCourses;
+        }catch(Exception exc){
+            // Logger.logException to centralized monitoring system
+        	   return false;
+				}
+    }
+}
+