import java.util.*;


public class DenseGraph extends Graph {
    private boolean[][] matrix;
    
    public DenseGraph(int n) {
        matrix = new boolean[n][n];
    }

    public boolean hasEdge(int p, int q) {
        return matrix[p][q];
    }

    public Set<Integer> edgesFrom(int p) {
        Set<Integer> result = new TreeSet<>();
        for (int i = 0; i < matrix[p].length; i++)
            if (matrix[p][i])
                result.add(i);
        return result;
    }

    public void addEdge(int p, int q) {
        matrix[p][q] = true;
        matrix[q][p] = true;
    }
}