import java.util.List;
import java.util.ArrayList;
import java.util.Map;
import java.util.Hashtable;
import java.util.Map.Entry;
class Graph{
public Map<String,List<String>> adjacentList= new Hashtable<String, List<String>>();
/**
* Adds a vertex to the graph.
* Returns true if added successfully or false if not.
* **/
public boolean addVertex(String vertex){
if (vertex ==null || vertex.isEmpty()){
System.out.println("The vertex cannot be null or empty.");
return false;
}
if (adjacentList.containsKey(vertex)){
System.out.println("Vertex "+vertex+" already exists.");
return false;
}
adjacentList.put(vertex, new ArrayList<String>());
return true;
}
/**
* Adds an edge between existing verteces.
* Returns true if added successfully or false if not.
* **/
public boolean addEdge(String node, String edge){
if (node == null || node.isEmpty()){
System.out.println("The start of the edge cannot be null or empty.");
return false;
}
if (edge == null || edge.isEmpty()){
System.out.println("The end of the edge cannot be null or empty.");
return false;
}
if (!adjacentList.containsKey(node)){
System.out.println("The start vertex "+node+" does not exist.");
return false;
}
if (!adjacentList.containsKey(edge)){
System.out.println("The end vertex "+edge+" does not exist.");
return false;
}
adjacentList.get(node).add(edge);
adjacentList.get(edge).add(node);
return true;
}
/**
* Prints all the connections if not empty.
**/
public void showConnections(){
if (adjacentList== null || adjacentList.isEmpty()){
System.out.println("The graph is empty");
}
for (Map.Entry<String,List<String>> entry : adjacentList.entrySet()){
System.out.print(entry.getKey()+" --> ");
for (String value: entry.getValue()){
System.out.print(" "+value);
}
System.out.println(" ");
}
}
}
class Main {
public static void main(String[] args) {
Graph graph = new Graph();
graph.addVertex("0");
graph.addVertex("1");
graph.addVertex("2");
graph.addVertex("3");
graph.addVertex("4");
graph.addVertex("5");
graph.addVertex("6");
graph.addEdge("3", "1");
graph.addEdge("3", "4");
graph.addEdge("4", "2");
graph.addEdge("4", "5");
graph.addEdge("1", "2");
graph.addEdge("1", "0");
graph.addEdge("0", "2");
graph.addEdge("6", "5");
graph.showConnections();
}
}
