Chapter 28 Exercise 21, Introduction to Java Programming, Tenth Edition Y. Daniel LiangY.

28.21 (Display sets of connected circles) Modify Listing 28.10,
ConnectedCircles.java, to display sets of connected circles in different colors.
That is, if two circles are connected, they are displayed using the same color;
otherwise, they are not in same color, as shown in Figure  28.25. (Hint: See
Programming Exercise 28.4.)

import java.util.Collections;
import java.util.LinkedList;
import java.util.List;
import java.util.ArrayList;

import javax.swing.*;

import java.awt.*;
import java.awt.event.*;

public class Exercise21 extends JApplet {
 private static final long serialVersionUID = 1L;
 // Circles are stored in a list
 private List<Circle> circles = new ArrayList<Circle>();

 public Exercise21() {
  add(new CirclePanel()); // Add to circle panel to applet
 }

 /** Panel for displaying circles */
 class CirclePanel extends JPanel {
  private static final long serialVersionUID = 1L;

  public CirclePanel() {
   addMouseListener(new MouseAdapter() {
    @Override
    public void mouseReleased(MouseEvent e) {
     if (!isInsideACircle(e.getPoint())) { // Add a new circle
      circles.add(new Circle(e.getX(), e.getY()));
      repaint();
     }
    }
   });
  }

  /** Returns true if the point is inside an existing circle */
  private boolean isInsideACircle(Point p) {
   for (Circle circle : circles)
    if (circle.contains(p))
     return true;

   return false;
  }

  @Override
  protected void paintComponent(Graphics g) {
   if (circles.size() == 0)
    return; // Nothing to paint

   super.paintComponent(g);

   // Build the edges
   List<AbstractGraph.Edge> edges = new ArrayList<AbstractGraph.Edge>();
   for (int i = 0; i < circles.size(); i++)
    for (int j = i + 1; j < circles.size(); j++)
     if (circles.get(i).overlaps(circles.get(j))) {
      edges.add(new AbstractGraph.Edge(i, j));
      edges.add(new AbstractGraph.Edge(j, i));
     }

   // Create a graph with circles as vertices
   UnweightedGraph<Circle> graph = new UnweightedGraph<Circle>(edges, circles);
   List<List<Integer>> connectedCircles = graph.getConnectedComponents();

   for (List<Integer> list : connectedCircles) {
    if(list.size() == 1) {
     Circle circle = circles.get(list.get(0));
     int radius = circle.radius;
     g.drawOval(circle.x - radius, circle.y - radius, 2 * radius, 2 * radius);
    } else {
     g.setColor(new Color((int) (Math.random() * 256), (int) (Math.random() * 256), (int) (Math.random() * 256)));
     for (Integer integer : list) {
      Circle circle = circles.get(integer);
      int radius = circle.radius;
      g.fillOval(circle.x - radius, circle.y - radius, 2 * radius, 2 * radius);
     }
     g.setColor(Color.BLACK);
    }
   }
  }
 }

 private static class Circle {
  int radius = 20;
  int x, y;

  Circle(int x, int y) {
   this.x = x;
   this.y = y;
  }

  public boolean contains(Point p) {
   double d = distance(x, y, p.x, p.y);
   return d <= radius;
  }

  public boolean overlaps(Circle circle) {
   return distance(this.x, this.y, circle.x, circle.y) <= radius
     + circle.radius;
  }

  private static double distance(int x1, int y1, int x2, int y2) {
   return Math.sqrt((x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2));
  }
 }

 public static void main(String[] args) {
  JFrame frame = new JFrame();
  JApplet applet = new Exercise21();
  frame.add(applet);
  frame.setTitle("Exercise21");
  frame.setLocationRelativeTo(null);
  frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
  frame.setSize(600, 400);
  frame.setLocationRelativeTo(null);
  frame.setVisible(true);
 }

 static class UnweightedGraph<V> extends AbstractGraph<V> {
  /** Construct an empty graph */
  public UnweightedGraph() {
  }

  /** Construct a graph from edges and vertices stored in arrays */
  public UnweightedGraph(int[][] edges, V[] vertices) {
   super(edges, vertices);
  }

  /** Construct a graph from edges and vertices stored in List */
  public UnweightedGraph(List<Edge> edges, List<V> vertices) {
   super(edges, vertices);
  }

  /** Construct a graph for integer vertices 0, 1, 2 and edge list */
  public UnweightedGraph(List<Edge> edges, int numberOfVertices) {
   super(edges, numberOfVertices);
  }

  /** Construct a graph from integer vertices 0, 1, and edge array */
  public UnweightedGraph(int[][] edges, int numberOfVertices) {
   super(edges, numberOfVertices);
  }
 }

 static abstract class AbstractGraph<V> implements Graph<V> {
  protected List<V> vertices = new ArrayList<V>(); // Store vertices
  protected List<List<Integer>> neighbors = new ArrayList<List<Integer>>(); // Adjacency
                     // lists

  /** Construct an empty graph */
  protected AbstractGraph() {
  }

  /** Construct a graph from edges and vertices stored in arrays */
  protected AbstractGraph(int[][] edges, V[] vertices) {
   for (int i = 0; i < vertices.length; i++)
    this.vertices.add(vertices[i]);

   createAdjacencyLists(edges, vertices.length);
  }

  /** Construct a graph from edges and vertices stored in List */
  protected AbstractGraph(List<Edge> edges, List<V> vertices) {
   for (int i = 0; i < vertices.size(); i++)
    this.vertices.add(vertices.get(i));

   createAdjacencyLists(edges, vertices.size());
  }

  /** Construct a graph for integer vertices 0, 1, 2 and edge list */
  @SuppressWarnings("unchecked")
  protected AbstractGraph(List<Edge> edges, int numberOfVertices) {
   for (int i = 0; i < numberOfVertices; i++)
    vertices.add((V) (new Integer(i))); // vertices is {0, 1, ...}

   createAdjacencyLists(edges, numberOfVertices);
  }

  /** Construct a graph from integer vertices 0, 1, and edge array */
  @SuppressWarnings("unchecked")
  protected AbstractGraph(int[][] edges, int numberOfVertices) {
   for (int i = 0; i < numberOfVertices; i++)
    vertices.add((V) (new Integer(i))); // vertices is {0, 1, ...}

   createAdjacencyLists(edges, numberOfVertices);
  }
  
  public List<List<Integer>> getConnectedComponents() {
   boolean[] isVisited = new boolean[vertices.size()];
   List<List<Integer>> result = new ArrayList<>();
   for (int i = 0; i < vertices.size(); i++) {
    if(!isVisited[i]) {
     List<Integer> newList = getConnectedComponents(i, isVisited);
     Collections.sort(newList);
     result.add(newList);
    }
   }
   return result;
  }
  
  public List<Integer> getConnectedComponents(int v, boolean[] isVisited) {
   List<Integer> searchOrder = new ArrayList<Integer>();
   LinkedList<Integer> stack = new LinkedList<>();
   stack.push(v);   
   while(!stack.isEmpty()) {
    int newV = stack.pop();
    if(!isVisited[newV]) {
     searchOrder.add(newV);
     isVisited[newV] = true;
     for (int i : neighbors.get(newV)) {
      if (!isVisited[i]) {
       stack.push(i);
      }
     }
    }
   }
   return searchOrder;
  }
  

  /** Create adjacency lists for each vertex */
  private void createAdjacencyLists(int[][] edges, int numberOfVertices) {
   // Create a linked list
   for (int i = 0; i < numberOfVertices; i++) {
    neighbors.add(new ArrayList<Integer>());
   }

   for (int i = 0; i < edges.length; i++) {
    int u = edges[i][0];
    int v = edges[i][1];
    neighbors.get(u).add(v);
   }
  }

  /** Create adjacency lists for each vertex */
  private void createAdjacencyLists(List<Edge> edges, int numberOfVertices) {
   // Create a linked list for each vertex
   for (int i = 0; i < numberOfVertices; i++) {
    neighbors.add(new ArrayList<Integer>());
   }

   for (Edge edge : edges) {
    neighbors.get(edge.u).add(edge.v);
   }
  }

  @Override
  /** Return the number of vertices in the graph */
  public int getSize() {
   return vertices.size();
  }

  @Override
  /** Return the vertices in the graph */
  public List<V> getVertices() {
   return vertices;
  }

  @Override
  /** Return the object for the specified vertex */
  public V getVertex(int index) {
   return vertices.get(index);
  }

  @Override
  /** Return the index for the specified vertex object */
  public int getIndex(V v) {
   return vertices.indexOf(v);
  }

  @Override
  /** Return the neighbors of the specified vertex */
  public List<Integer> getNeighbors(int index) {
   return neighbors.get(index);
  }

  @Override
  /** Return the degree for a specified vertex */
  public int getDegree(int v) {
   return neighbors.get(v).size();
  }

  @Override
  /** Print the edges */
  public void printEdges() {
   for (int u = 0; u < neighbors.size(); u++) {
    System.out.print(getVertex(u) + " (" + u + "): ");
    for (int j = 0; j < neighbors.get(u).size(); j++) {
     System.out.print("(" + u + ", " + neighbors.get(u).get(j)
       + ") ");
    }
    System.out.println();
   }
  }

  @Override
  /** Clear graph */
  public void clear() {
   vertices.clear();
   neighbors.clear();
  }

  @Override
  /** Add a vertex to the graph */
  public void addVertex(V vertex) {
   vertices.add(vertex);
   neighbors.add(new ArrayList<Integer>());
  }

  @Override
  /** Add an edge to the graph */
  public void addEdge(int u, int v) {
   neighbors.get(u).add(v);
   neighbors.get(v).add(u);
  }

  /** Edge inner class inside the AbstractGraph class */
  public static class Edge {
   public int u; // Starting vertex of the edge
   public int v; // Ending vertex of the edge

   /** Construct an edge for (u, v) */
   public Edge(int u, int v) {
    this.u = u;
    this.v = v;
   }
  }

  @Override
  /** Obtain a DFS tree starting from vertex v */
  /** To be discussed in Section 27.6 */
  public Tree dfs(int v) {
   List<Integer> searchOrder = new ArrayList<Integer>();
   int[] parent = new int[vertices.size()];
   for (int i = 0; i < parent.length; i++)
    parent[i] = -1; // Initialize parent[i] to -1

   // Mark visited vertices
   boolean[] isVisited = new boolean[vertices.size()];

   // Recursively search
   dfs(v, parent, searchOrder, isVisited);

   // Return a search tree
   return new Tree(v, parent, searchOrder);
  }

  /** Recursive method for DFS search */
  private void dfs(int v, int[] parent, List<Integer> searchOrder,
    boolean[] isVisited) {
   // Store the visited vertex
   searchOrder.add(v);
   isVisited[v] = true; // Vertex v visited

   for (int i : neighbors.get(v)) {
    if (!isVisited[i]) {
     parent[i] = v; // The parent of vertex i is v
     dfs(i, parent, searchOrder, isVisited); // Recursive search
    }
   }
  }

  @Override
  /** Starting bfs search from vertex v */
  /** To be discussed in Section 27.7 */
  public Tree bfs(int v) {
   List<Integer> searchOrder = new ArrayList<Integer>();
   int[] parent = new int[vertices.size()];
   for (int i = 0; i < parent.length; i++)
    parent[i] = -1; // Initialize parent[i] to -1

   java.util.LinkedList<Integer> queue = new java.util.LinkedList<Integer>(); // list
                      // used
                      // as
                      // a
                      // queue
   boolean[] isVisited = new boolean[vertices.size()];
   queue.offer(v); // Enqueue v
   isVisited[v] = true; // Mark it visited

   while (!queue.isEmpty()) {
    int u = queue.poll(); // Dequeue to u
    searchOrder.add(u); // u searched
    for (int w : neighbors.get(u)) {
     if (!isVisited[w]) {
      queue.offer(w); // Enqueue w
      parent[w] = u; // The parent of w is u
      isVisited[w] = true; // Mark it visited
     }
    }
   }

   return new Tree(v, parent, searchOrder);
  }

  /** Tree inner class inside the AbstractGraph class */
  /** To be discussed in Section 27.5 */
  public class Tree {
   private int root; // The root of the tree
   private int[] parent; // Store the parent of each vertex
   private List<Integer> searchOrder; // Store the search order

   /** Construct a tree with root, parent, and searchOrder */
   public Tree(int root, int[] parent, List<Integer> searchOrder) {
    this.root = root;
    this.parent = parent;
    this.searchOrder = searchOrder;
   }

   /** Return the root of the tree */
   public int getRoot() {
    return root;
   }

   /** Return the parent of vertex v */
   public int getParent(int v) {
    return parent[v];
   }

   /** Return an array representing search order */
   public List<Integer> getSearchOrder() {
    return searchOrder;
   }

   /** Return number of vertices found */
   public int getNumberOfVerticesFound() {
    return searchOrder.size();
   }

   /** Return the path of vertices from a vertex to the root */
   public List<V> getPath(int index) {
    ArrayList<V> path = new ArrayList<V>();

    do {
     path.add(vertices.get(index));
     index = parent[index];
    } while (index != -1);

    return path;
   }

   /** Print a path from the root to vertex v */
   public void printPath(int index) {
    List<V> path = getPath(index);
    System.out.print("A path from " + vertices.get(root) + " to "
      + vertices.get(index) + ": ");
    for (int i = path.size() - 1; i >= 0; i--)
     System.out.print(path.get(i) + " ");
   }

   /** Print the whole tree */
   public void printTree() {
    System.out.println("Root is: " + vertices.get(root));
    System.out.print("Edges: ");
    for (int i = 0; i < parent.length; i++) {
     if (parent[i] != -1) {
      // Display an edge
      System.out.print("(" + vertices.get(parent[i]) + ", "
        + vertices.get(i) + ") ");
     }
    }
    System.out.println();
   }
  }
 }

 interface Graph<V> {
  /** Return the number of vertices in the graph */
  public int getSize();

  /** Return the vertices in the graph */
  public java.util.List<V> getVertices();

  /** Return the object for the specified vertex index */
  public V getVertex(int index);

  /** Return the index for the specified vertex object */
  public int getIndex(V v);

  /** Return the neighbors of vertex with the specified index */
  public java.util.List<Integer> getNeighbors(int index);

  /** Return the degree for a specified vertex */
  public int getDegree(int v);

  /** Print the edges */
  public void printEdges();

  /** Clear graph */
  public void clear();

  /** Add a vertex to the graph */
  public void addVertex(V vertex);

  /** Add an edge to the graph */
  public void addEdge(int u, int v);

  /** Obtain a depth-first search tree */
  public AbstractGraph<V>.Tree dfs(int v);

  /** Obtain a breadth-first search tree */
  public AbstractGraph<V>.Tree bfs(int v);
 }

}