Given n coins and a pan balance,find the only counterfeit 4

The Utils class is composed of some common methods:

java 代码

 

1. package solve;  
2.   
3. import scale.Ball;  
4. import scale.Scale;  
5.   
6. import java.util.Iterator;  
7. import java.util.Set;  
8.   
9. /** 
10.  * utility class, shared common methods. 
11.  */  
12. public class Utils  
13. {  
14.     public static Ball findGoodBall(Set ballSet)  
15.     {  
16.         for (Iterator it=ballSet.iterator(); it.hasNext();)  
17.         {  
18.             Ball ball = (Ball)it.next();  
19.             if (ball.getStatus().equals(Ball.NORMAL)) return ball;  
20.         }  
21.   
22.         return null;  
23.     }  
24.   
25.     public static String convertToBallStatus(int scaleResult)  
26.     {  
27.         if (scaleResult == Scale.EVEN) return Ball.NORMAL;  
28.         else if (scaleResult == Scale.HEAVIER) return Ball.HEAVIER;  
29.         else return Ball.LIGHTER;  
30.     }  
31.   
32.     public static void markStatus(Set ballSet, String status)  
33.     {  
34.         for (Iterator it=ballSet.iterator(); it.hasNext();)  
35.         {  
36.             Ball ball = (Ball)it.next();  
37.             if (!ball.getStatus().equals(Ball.NORMAL))  
38.             {  
39.                 ball.setStatus(status);  
40.             }  
41.         }  
42.     }  
43. }  

The test class is as follows:

java 代码

 

1. package solve;  
2.   
3. import junit.framework.TestCase;  
4.   
5. import java.util.Set;  
6. import java.util.HashSet;  
7. import java.util.Iterator;  
8. import java.math.BigDecimal;  
9.   
10. import scale.Ball;  
11. import scale.Weight;  
12. import scale.Scale;  
13.   
14. /** 
15.  * 
16.  */  
17. public class SolverTest extends TestCase  
18. {  
19.     public void test12Balls()  
20.     {  
21.         Set ballSet = createBallSet(12, 4, Ball.WEIGHT_HEAVIER);  
22.         ProblemSolver solver = new ProblemSolver(ballSet);  
23.         solver.findWeight();  
24.   
25.         print(ballSet);  
26.         System.out.println("scale usage=" + solver.getScale().getNumOfTrials());  
27.         verifyResult(ballSet, solver.getScale());  
28.     }  
29.   
30.     public void test13Balls()  
31.     {  
32.         Set ballSet = createBallSet(13, 5, Ball.WEIGHT_HEAVIER);  
33.         ProblemSolver solver = new ProblemSolver(ballSet);  
34.         solver.findWeight();  
35.   
36.         print(ballSet);  
37.         System.out.println("scale usage=" + solver.getScale().getNumOfTrials());  
38.         verifyResult(ballSet, solver.getScale());  
39.     }  
40.   
41.     public void testLoops()  
42.     {  
43.         int start = 500;  
44.         int end = 1000;  
45.         for (int i=start; i
46.         {  
47.             for (int j=0; j
48.             {  
49.                 Set ballSet = createBallSet(i, j, Ball.WEIGHT_HEAVIER);  
50.                 ProblemSolver solver = new ProblemSolver(ballSet);  
51.                 solver.findWeight();  
52.   
53.                 System.out.println("num of balls=" + ballSet.size());  
54.                 //print(ballSet);  
55.                 System.out.println("scale usage=" + solver.getScale().getNumOfTrials());  
56.                 System.out.println("-------------------------------------------------");  
57.                 verifyResult(ballSet, solver.getScale());  
58.             }  
59.         }  
60.     }  
61.     private Set createBallSet(int size, int badBallIndex, Weight weight)  
62.     {  
63.         Set ballSet = new HashSet();  
64.         for (int i=0; i
65.         {  
66.             Weight weight1;  
67.             if (i == badBallIndex) weight1 = weight;  
68.             else weight1 = Ball.WEIGHT_NORNAL;  
69.             Ball ball = new Ball("" + i, weight1);  
70.             ballSet.add(ball);  
71.         }  
72.   
73.         return ballSet;  
74.     }  
75.   
76.     private void verifyResult(Set ballSet, Scale scale)  
77.     {  
78.         for (Iterator it=ballSet.iterator(); it.hasNext();)  
79.         {  
80.             Ball ball = (Ball)it.next();  
81.             assertTrue(ball.validate());  
82.         }  
83.   
84.         // now computer the theoretic limit number of balls <=(3^n-3)/2, upper limit.  
85.         // Number of balls  3  12  39  120  363  1092 3279 .....  
86.         // Number of trials 2  3   4   5    6    7    8  
87.         BigDecimal aa = new BigDecimal(Math.log(2 * ballSet.size() + 3));  
88.         BigDecimal bb = aa.divide(new BigDecimal(Math.log(3)), BigDecimal.ROUND_UP);  
89.         int limit = (int)Math.ceil(bb.floatValue());  
90.         assertTrue("limit=" + limit + ", trials=" + scale.getNumOfTrials(), limit >= scale.getNumOfTrials());  
91.     }  
92.   
93.     private void print(Set ballSet)  
94.     {  
95.         for (Iterator it=ballSet.iterator(); it.hasNext();)  
96.         {  
97.             Ball ball = (Ball)it.next();  
98.             System.out.println(ball.toString());  
99.         }  
100.     }  
101. }  

The testing is a little hard because of the recursion. Any change requires a full test. The testing checks whether the status flags we set matches the weights from the input and the times of weighings stays inside the limit.