Question

我必须编写一个c ++程序，但只有以下部分存在问题：

[...]为此目的，您将需要两个随机整数集合{0,1，...，9}上的均匀分布（这两个数字必须是以相同的概率生成）[...]

我不知道数学和c ++一样好，我也不允许使用c ++ 11。我写了以下简单的代码，但我怀疑它是否正确？：P

package javaapplication1;
import java.awt.*;
import java.io.*;
import java.sql.*;
import java.util.*;
import javax.swing.*;
import static javax.swing.JFrame.EXIT_ON_CLOSE;
import javax.swing.table.*;

public class TableD extends javax.swing.JFrame {
    public TableD() {
        initComponents();


Vector columnNames = new Vector();
Vector data = new Vector();

try {
Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
Connection connect =DriverManager.getConnection("jdbc:odbc:cb1");

String sql = "Select * from tblbooks";
Statement stmt = connect.createStatement();
ResultSet rs = stmt.executeQuery( sql );
ResultSetMetaData md = rs.getMetaData();
int columns = md.getColumnCount();
for (int i = 1; i <= columns; i++) {
columnNames.addElement( md.getColumnName(i) );

}
while (rs.next()) {
Vector row = new Vector(columns);
for (int i = 1; i <= columns; i++) {
row.addElement( rs.getObject(i) );
}
data.addElement( row );

}
rs.close();
stmt.close();
}
catch(Exception e) {
System.out.println( e );
}
JTable table = new JTable(data, columnNames);

//JScrollPane scrollPane = new JScrollPane( table );
//getContentPane().add( scrollPane );

//JPanel buttonPanel = new JPanel();
//getContentPane().add( buttonPanel, BorderLayout.SOUTH );
    }
    /**
     * This method is called from within the constructor to initialize the form.
     * WARNING: Do NOT modify this code. The content of this method is always
     * regenerated by the Form Editor.
     */
    @SuppressWarnings("unchecked")
    // <editor-fold defaultstate="collapsed" desc="Generated Code">                          
    private void initComponents() {

        jScrollPane1 = new javax.swing.JScrollPane();
        jTable1 = new javax.swing.JTable();

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);

        jTable1.setModel(new javax.swing.table.DefaultTableModel(
            new Object [][] {
                {null, null, null, null},
                {null, null, null, null},
                {null, null, null, null},
                {null, null, null, null}
            },
            new String [] {
                "Title 1", "Title 2", "Title 3", "Title 4"
            }
        ));
        jScrollPane1.setViewportView(jTable1);

        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(javax.swing.GroupLayout.Alignment.TRAILING, layout.createSequentialGroup()
                .addContainerGap(15, Short.MAX_VALUE)
                .addComponent(jScrollPane1, javax.swing.GroupLayout.PREFERRED_SIZE, 375, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addContainerGap())
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addContainerGap()
                .addComponent(jScrollPane1, javax.swing.GroupLayout.PREFERRED_SIZE, 275, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addContainerGap(14, Short.MAX_VALUE))
        );

        pack();
    }// </editor-fold>                        

    /**
     * @param args the command line arguments
     */
    public static void main(String args[]) {
        /* Set the Nimbus look and feel */
        //<editor-fold defaultstate="collapsed" desc=" Look and feel setting code (optional) ">
        /* If Nimbus (introduced in Java SE 6) is not available, stay with the default look and feel.
         * For details see http://download.oracle.com/javase/tutorial/uiswing/lookandfeel/plaf.html 
         */
        try {
            for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) {
                if ("Nimbus".equals(info.getName())) {
                    javax.swing.UIManager.setLookAndFeel(info.getClassName());
                    break;
                }
            }
        } catch (ClassNotFoundException ex) {
            java.util.logging.Logger.getLogger(TableD.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (InstantiationException ex) {
            java.util.logging.Logger.getLogger(TableD.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (IllegalAccessException ex) {
            java.util.logging.Logger.getLogger(TableD.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (javax.swing.UnsupportedLookAndFeelException ex) {
            java.util.logging.Logger.getLogger(TableD.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        }
        //</editor-fold>
        TableD frame = new TableD();
/*frame.setDefaultCloseOperation( EXIT_ON_CLOSE );
frame.pack();
frame.setTitle("Information Table");
frame.setVisible(true);*/


        /* Create and display the form */
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new TableD().setVisible(true);
            }
        });
    }

    // Variables declaration - do not modify                     
    private javax.swing.JScrollPane jScrollPane1;
    private javax.swing.JTable jTable1;
    // End of variables declaration                   
}

Answer 1

每个程序只调用一次x y z 1: Pre A Lorem ipsum dolor sit amet, ac 2: Pre C Maecenas netus in, lacus fames 3: Pre C Conubia sed nulla dolor dui ap 4: Pre A Eget laoreet eros in aliquet e 5: Pre A Vestibulum quisque himenaeos p 6: Post A Sed venenatis. Ante turpis ege 7: Post A Ultricies ultricies eleifend m 8: Post B Conubia in in sed etiam nec mo 9: Post A Quam nec ex sodales dictum orc 10: Post A Sed ante id pulvinar maximus s，而不是每次都需要一个随机数。对随机数使用模数技巧通常不会给出均匀分布。所以不，解决方案可能不正确。

Answer 2

这取决于你是否真的需要它，或者只是非常接近。你的解决方案很接近，但并不完美。

假设您使用的是Microsoft的C ++，其中有RAND_MAX of only 32767。获得0到7的几率为3277/32768，而获得8或9的几率仅为3276/32768。

StackOverflow上有很多关于如何获得完美分发的问题，例如：What is the optimal algorithm for generating an unbiased random integer within a range?

均匀分布的随机整数

2 个答案: