Chapter 22 Exercise 19, Introduction to Java Programming, Tenth Edition Y. Daniel LiangY.

22.19 (Largest block) The problem for finding a largest block is described in Programming Exercise 8.35. Design a dynamic programming algorithm for solv-
ing this problem in O(n 2 ) time. Write a test program that displays a 10-by-10
square matrix, as shown in Figure 22.14a. Each element in the matrix is 0 or
1, randomly generated with a click of the Refresh button. Display each number
centered in a text field. Use a text field for each entry. Allow the user to change
the entry value. Click the Find Largest Block button to find a largest square
submatrix that consists of 1s. Highlight the numbers in the block, as shown in
Figure  22.14b.

import javax.swing.*;
import javax.swing.border.LineBorder;

import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;


public class Exercise19 extends JApplet {

 private static final long serialVersionUID = 1L;
 private int arrSize = 10;
 private JTextField[] jTextFields = new JTextField[arrSize * arrSize];

 public Exercise19() {
  JPanel jPanel1 = new JPanel(new GridLayout(arrSize, arrSize));
  jPanel1.setBorder(new LineBorder(Color.BLACK));
  for (int i = 0; i < jTextFields.length; i++) {
   jTextFields[i] = new JTextField((Math.random() < 0.5 ? "0" : "1"), 3);
   jTextFields[i].setHorizontalAlignment(JTextField.CENTER);
   jTextFields[i].setFont(new Font("Monospaced", Font.BOLD, 20));
   jPanel1.add(jTextFields[i]);
  }
  add(jPanel1, BorderLayout.CENTER);
  JPanel jPanel2 = new JPanel();
  JButton jButton1 = new JButton("Refresh");
  jPanel2.add(jButton1);
  JButton jButton2 = new JButton("Find Largest Block");
  jPanel2.add(jButton2);
  add(jPanel2, BorderLayout.SOUTH);
  
  jButton1.addActionListener(new ActionListener() {   
   @Override
   public void actionPerformed(ActionEvent e) {
    for (int i = 0; i < jTextFields.length; i++) {
     jTextFields[i].setText((Math.random() < 0.5 ? "0" : "1"));
     jTextFields[i].setForeground(Color.BLACK);
    }
   }
  });
  
  jButton2.addActionListener(new ActionListener() {   
   @Override
   public void actionPerformed(ActionEvent e) {
    int[][] data = new int[arrSize][arrSize];
    for (int i = 0; i < arrSize; i++) {
     for (int j = 0; j < arrSize; j++) {
      jTextFields[i * arrSize + j].setForeground(Color.BLACK);
      data[i][j] = Integer.parseInt(jTextFields[i * arrSize + j].getText());
     }
    }
    
    int[] result = findLargestBlock(data);
    
    for (int i = result[0]; i < result[0] + result[2]; i++) {
     for (int j =  result[1]; j < result[1] + result[2]; j++) {
      jTextFields[i * arrSize + j].setForeground(Color.RED);
     }
    }   
    
   }
  });
 }
 
 
 public static int[] findLargestBlock(int[][] m) {
  int[] submatrix = new int[3];
  for (int i = 0; i < m.length; i++) {
   for (int j = 0; j < m[i].length; j++) {
    if (m[i][j] == 1) {
     int size = getSubMatrixSize(i, j, m);
     if (size > submatrix[2]) {
      submatrix[0] = i;
      submatrix[1] = j;
      submatrix[2] = size;
     }
     
    }
   }
  }
  return submatrix;
 }
 
 
 public static int getSubMatrixSize(int row, int column, int[][] m) {
  int result = 0;
  for (int i = row; i < m.length; i++) {
   for (int j = column; j < m[i].length; j++) {
    for (int size = 1; size < m.length; size++) {
     if (!isAll1s(row, column, size, m)) {
      if (result < (size - 1)) {
       result = size - 1;
      }
      break;
     }
    }
   }
  }
  return result;
 }
 
 public static boolean isAll1s(int row, int column, int size, int[][] m) {
  for (int i = row; i < row + size; i++) {
   if (i >= m.length) {
    return false;
   }
   for (int j = column; j < column + size; j++) {
    if (j >= m[i].length) {
     return false;
    }
    if (m[i][j] != 1) {
     return false;
    }

   }
  }
  return true;
 }
 
 public static void main(String[] args) {
  JFrame frame = new JFrame("Exercise19");
  Exercise19 applet = new Exercise19();
  frame.add(applet);
  frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
  frame.pack();
  frame.setMinimumSize(new Dimension(frame.getWidth(), frame.getHeight()));
  frame.setLocationRelativeTo(null);
  frame.setVisible(true);
 }
}