lotterydrawing.java

Core Java《Java核心技术》课后习题

/**
   @version 1.20 2004-02-10
   @author Cay Horstmann
*/

import java.util.*;

public class LotteryDrawing
{  
   public static void main(String[] args)
   {  
      Scanner in = new Scanner(System.in);

      System.out.print("How many numbers do you need to draw? ");
      int k = in.nextInt();
      
      System.out.print("What is the highest number you can draw? ");
      int n = in.nextInt();

      // fill an array with numbers 1 2 3 . . . n
      int[] numbers = new int[n];
      for (int i = 0; i < numbers.length; i++)
         numbers[i] = i + 1;

      // draw k numbers and put them into a second array
      int[] result = new int[k];
      for (int i = 0; i < result.length; i++)
      {  
         // make a random index between 0 and n - 1
         int r = (int) (Math.random() * n);

         // pick the element at the random location
         result[i] = numbers[r];

         // move the last element into the random location
         numbers[r] = numbers[n - 1];
         n--;
      }

      // print the sorted array
      Arrays.sort(result);
      System.out.println("Bet the following combination. It'll make you rich!");
      for (int r : result)
         System.out.println(r);
   }
}