import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;
import java.util.stream.Collectors;
import java.util.stream.Stream;
public class Digraph {
private Map<Integer, Set<Integer>> neighbors = new HashMap<>();
public Set<Integer> getPoints() {
Set<Integer> points = neighbors.keySet().stream().collect(Collectors.toCollection(HashSet::new));
this.neighbors.values().forEach(i -> points.addAll(i));
return points;
}
public int size() {
return getPoints().size();
}
public long edgeSize() {
return neighbors.values().stream().collect(Collectors.summingLong(Set::size));
}
public void addEdge(int a, int b) {
neighbors.computeIfAbsent(a, k -> new HashSet<Integer>()).add(b);
//neighbors.computeIfAbsent(b, k -> new HashSet<Integer>()).add(a);
}
public static void main(String...args) {
Digraph g = new Digraph();
for(int i = 0; i < 6; i++) {
g.addEdge(i, i + 1);
g.addEdge(i, i + 2);
}
System.out.println("strict digraph {");
g.neighbors.keySet().stream().forEach(i ->
{
Stream.of(g.neighbors.get(i)).flatMap(j -> j.stream())
.forEach(k -> System.out.println(i + "->" + k));
});
System.out.println("}");
System.out.println("number of points: " + g.size());
System.out.println("number of edges: " + g.edgeSize());
}
}
