Interviewer basically wanted the count of all reciprocated edges and way to store these edges.

He pasted the below code snippets and wanted me implemented these methods. I gave a solution which involved storing the reciprocated edges in a map. But go to know I was rejected :-(

// Get an object representing the edge

// from the node with ID "a"

// to the node with ID "b"

// returns null if no edge exists

//List...

Edge e = graph.getEdge("a", "b");

// arbitrary data stored on the edge

EdgeData eData = e.getData();

// IDs of source and destination nodes

String sourceId = e.getSourceId();

String destinationId = e.getDestinationId();

for (Edge edge : graph.getAllEdges()) {

// executes once per edge of the graph in arbitrary order

}

/**

• Returns the number of reciprocated edges in the given directed graph.

• A reciprocated edge is a pair of nodes (X, Y) such that there is an edge

• from X to Y and an edge from Y to X.

*/

int <NODE_DATA, EDGE_DATA> countReciprocatedEdges(

DirectedGraph<NODE_DATA, EDGE_DATA> graph) {

// implementation here

}

return countReciprocatedEdges;

a -> b

b -> a

b -> c

c -> a

// create an empty graph

DirectedGraph<NodeData, EdgeData> g = new DirectedGraph<>();

// Create nodes named "a", and "b", each with associated data

g.addNode("a", aNodeData);

g.addNode("b", bNodeData);

// return node with given name or null if none exists

Node nodeA = g.getNode("a");

// Create an edge from "a" to "b" with arbitrary associated data

g.addEdge("a", "b", abEdgeData);

class Node<NODE_DATA> {

private NODE_DATA data;

private String id;

Node<NODE_DATA>(String id, NODE_DATA data) {

this.data = data;

this.id = id;

}

public NODE_DATA getData() {

return data;

}

public String getId() {

return id;

}

}

class Edge<EDGE_DATA> {

Edge(String sourceId, String dstId, EDGE_DATA edgeData) {

this.sourceId = sourceId;

this.dstId = dstId;

this.edgeData = edgeData;

}

}

Edge e = new Edge("a", "b", "edgeData");

class DirectedGraph<NODE_DATA, EDGE_DATA> {

//List<Edge<EDGE_DATA>> edges = new ArrayList<Edge<EDGE_DATA>>();

public void addEdge(String source, String destination, EDGE_DATA edgeData){

}

public Edge getEdge(String source, dest){

}

public List getAllEdges(){

}