class Graph {
HashMap<String,List<String>>graph;
public Graph(){
graph = new HashMap<>();
}
public void addVertex(String v){
graph.putIfAbsent(v,new ArrayList<>());
}
public void addEdge(String v1, String v2){
graph.get(v1).add(v2);
}
public void printGraph(){
for(String key : graph.keySet()){
System.out.print(key+" : ");
List<String> temp = graph.get(key);
if(temp.isEmpty())System.out.print("NULL");
for(String buff : temp){
System.out.print(buff+" ");
}
System.out.println();
}
}
}
