bigintegertest.java

Java核心技术 卷一 的配套源代码!!绝对全

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

import java.math.*;
import java.util.*;

public class BigIntegerTest
{  
   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();

      /* 
         compute binomial coefficient
         n * (n - 1) * (n - 2) * . . . * (n - k + 1)
         -------------------------------------------
         1 * 2 * 3 * . . . * k
      */

      BigInteger lotteryOdds = BigInteger.valueOf(1);

      for (int i = 1; i <= k; i++)
         lotteryOdds = lotteryOdds
            .multiply(BigInteger.valueOf(n - i + 1))
            .divide(BigInteger.valueOf(i));

      System.out.println("Your odds are 1 in " + lotteryOdds + ". Good luck!");
   }
}