corejava第10版

corejava第10版/v1ch03/BigIntegerTest/BigIntegerTest.java

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+import java.math.*;
+import java.util.*;
+
+/**
+ * This program uses big numbers to compute the odds of winning the grand prize in a lottery.
+ * @version 1.20 2004-02-10
+ * @author Cay Horstmann
+ */
+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!");
+   }
+}