make BFS iterative

mapbuilder/src/main/java/map/builder/utilities/ConnectedComponentGraph.java

@@ -63,6 +63,44 @@ public class ConnectedComponentGraph {
         return list;
     }
 
+    public ArrayList<Long> DFS(Long s, HashMap<Long, Boolean> visited) {
+        // Create a stack for DFS
+        Stack<Long> stack = new Stack<Long>();
+        ArrayList<Long> vertices = new ArrayList<Long>();
+
+        // Push the current source node
+        stack.push(s);
+
+        while (stack.empty() == false) {
+            // Pop a vertex from stack and print it
+            s = stack.peek();
+            stack.pop();
+
+            // Stack may contain same vertex twice. So
+            // we need to print the popped item only
+            // if it is not visited.
+            if (visited.get(s) == false) {
+                System.out.print(s + " ");
+                visited.put(s, true);
+                vertices.add(s);
+            }
+
+            // Get all adjacent vertices of the popped vertex s
+            // If a adjacent has not been visited, then push it
+            // to the stack.
+            Iterator<Long> itr = adj.get(s).iterator();
+
+            while (itr.hasNext()) {
+                Long v = itr.next();
+                if (!visited.get(v))
+                    stack.push(v);
+            }
+
+        }
+
+        return vertices;
+    }
+
     // Function that returns reverse (or transpose) of this ConnectedComponentGraph
     public ConnectedComponentGraph getTranspose() {
         ConnectedComponentGraph g = new ConnectedComponentGraph();
@@ -130,7 +168,7 @@ public class ConnectedComponentGraph {
 
             // Print Strongly connected component of the popped vertex
             if (visited.get(v) == false) {
-                ArrayList<Long> component = gr.DFSUtil(v, visited);
+                ArrayList<Long> component = gr.DFS(v, visited);
                 if (maxLength < component.size()) {
                     maxLength = component.size();
                     largestComponent = component;