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

最新推荐文章于 2025-11-24 15:28:22 发布

最新推荐文章于 2025-11-24 15:28:22 发布 · 148 阅读

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#Java #junit #J# #UP

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本文介绍了一个用于检测一组球中异常重量球的算法实现。通过递归地将球分为几组并使用天平进行称重比较，算法能有效地找出较重或较轻的球。文章包含详细的Java代码示例及单元测试。

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The Utils class is composed of some common methods:

java 代码

package solve;
import scale.Ball;
import scale.Scale;
import java.util.Iterator;
import java.util.Set;
/**
* utility class, shared common methods.
*/
public class Utils
{
public static Ball findGoodBall(Set ballSet)
{
for (Iterator it=ballSet.iterator(); it.hasNext();)
{
Ball ball = (Ball)it.next();
if (ball.getStatus().equals(Ball.NORMAL)) return ball;
}
return null;
}
public static String convertToBallStatus(int scaleResult)
{
if (scaleResult == Scale.EVEN) return Ball.NORMAL;
else if (scaleResult == Scale.HEAVIER) return Ball.HEAVIER;
else return Ball.LIGHTER;
}
public static void markStatus(Set ballSet, String status)
{
for (Iterator it=ballSet.iterator(); it.hasNext();)
{
Ball ball = (Ball)it.next();
if (!ball.getStatus().equals(Ball.NORMAL))
{
ball.setStatus(status);
}
}
}
}

The test class is as follows:

java 代码

package solve;
import junit.framework.TestCase;
import java.util.Set;
import java.util.HashSet;
import java.util.Iterator;
import java.math.BigDecimal;
import scale.Ball;
import scale.Weight;
import scale.Scale;
/**
*
*/
public class SolverTest extends TestCase
{
public void test12Balls()
{
Set ballSet = createBallSet(12, 4, Ball.WEIGHT_HEAVIER);
ProblemSolver solver = new ProblemSolver(ballSet);
solver.findWeight();
print(ballSet);
System.out.println("scale usage=" + solver.getScale().getNumOfTrials());
verifyResult(ballSet, solver.getScale());
}
public void test13Balls()
{
Set ballSet = createBallSet(13, 5, Ball.WEIGHT_HEAVIER);
ProblemSolver solver = new ProblemSolver(ballSet);
solver.findWeight();
print(ballSet);
System.out.println("scale usage=" + solver.getScale().getNumOfTrials());
verifyResult(ballSet, solver.getScale());
}
public void testLoops()
{
int start = 500;
int end = 1000;
for (int i=start; i
{
for (int j=0; j
{
Set ballSet = createBallSet(i, j, Ball.WEIGHT_HEAVIER);
ProblemSolver solver = new ProblemSolver(ballSet);
solver.findWeight();
System.out.println("num of balls=" + ballSet.size());
//print(ballSet);
System.out.println("scale usage=" + solver.getScale().getNumOfTrials());
System.out.println("-------------------------------------------------");
verifyResult(ballSet, solver.getScale());
}
}
}
private Set createBallSet(int size, int badBallIndex, Weight weight)
{
Set ballSet = new HashSet();
for (int i=0; i
{
Weight weight1;
if (i == badBallIndex) weight1 = weight;
else weight1 = Ball.WEIGHT_NORNAL;
Ball ball = new Ball("" + i, weight1);
ballSet.add(ball);
}
return ballSet;
}
private void verifyResult(Set ballSet, Scale scale)
{
for (Iterator it=ballSet.iterator(); it.hasNext();)
{
Ball ball = (Ball)it.next();
assertTrue(ball.validate());
}
// now computer the theoretic limit number of balls <=(3^n-3)/2, upper limit.
// Number of balls 3 12 39 120 363 1092 3279 .....
// Number of trials 2 3 4 5 6 7 8
BigDecimal aa = new BigDecimal(Math.log(2 * ballSet.size() + 3));
BigDecimal bb = aa.divide(new BigDecimal(Math.log(3)), BigDecimal.ROUND_UP);
int limit = (int)Math.ceil(bb.floatValue());
assertTrue("limit=" + limit + ", trials=" + scale.getNumOfTrials(), limit >= scale.getNumOfTrials());
}
private void print(Set ballSet)
{
for (Iterator it=ballSet.iterator(); it.hasNext();)
{
Ball ball = (Ball)it.next();
System.out.println(ball.toString());
}
}
}

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.

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