一道著名的概率问题的Java解法：电影《决胜21点》里的山羊问题 - FreeOZ论坛

1 import java.util.*;
2 import static java.lang.System.out;
3
4 public class LotoTest {
5 private static final int PARAM_NUM = 1;
6
7 private static void usage(){
8 out.println("Usage: java -cp <classpath> LotoTest <num>\n");
9 }
10
11 /*
12 * Algorithm:
13 * Giving an Array of 3 boolean, one and only one
14 * of them are true. Randomly pick up a value A[x].
15 * then the program unveal another one which is not
16 * true. Run the program to determine the possibility
17 * that A[x] is true and the possibility that A[rest]
18 * is true.
19 */
20 public static void main(String [] args){
21 if(args.length != PARAM_NUM) {
22 usage();
23 return;
24 }
25
26 int runNum = Integer.valueOf(args[0]);
27
28 //Create three randomizer
29 //One for value setting
30 //One for picking up value
31 //The other for unveal
32 Random ran01 = new Random(new Date().getTime());
33 Random ran02 = new Random(
34 LotoTest.class.hashCode()
35 * ran01.nextLong() * new Date().getTime());
36 Random ran03 = new Random(
37 LotoTest.class.hashCode()
38 * ran02.nextLong()
39 * ran01.nextLong() * new Date().getTime());
40
41 int pickHit = 0;
42
43 for(int runc=0; runc<runNum; ++runc) {
44 //Generate the position to store the true value
45 int pos = (int)(ran01.nextDouble() * 3);
46 //declare and initialize the boolean array to false
47 boolean A[] = new boolean[3];
48
49 A[pos] = true;
50
51 //pick up one position for lucky
52 int pickup = (int)(ran02.nextDouble() * 3);
53
54 //unveal one of the false position
55 int unveal = 0;
56
57 do{
58 unveal = (int)(ran03.nextDouble() * 3);
59 if(unveal == pickup)
60 continue;
61 if(unveal == pos)
62 continue;
63 break;
64 }while(true);
65
66 if(pickup == pos)
67 ++ pickHit;
68
69 }
70
71 out.printf("PickHit = %d, Other = %d, Total = %d\n",
72 pickHit, runNum - pickHit, runNum);
73 }
74 }

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