2016 9月 Algorithm，Part1 week3 作业帖

课程汇总 && 介绍：http://www.1point3acres.com/bbs/thread-200970-1-1.html

第三次作业，Collinear Points， 作业入口

哎改了好多遍 immutable那里始终通过不了
clone()也用了 还是不行...
现就这样了吧 心好累...

immutable的问题后来解决了。花了很长时间。跟各位分享下。
因为时间过去很久了，大致思路是，java程序的输入还是输出的array，一定要在程序内做个copy，不是仅仅copy reference，是把reference所指向的object也copy了。这样，当程序外面的array有变化的时候，不会影响程序内的数据，就是immutable的了！
这是一种所谓的best practice吧。
以上供参考

程序里还有两个错误一直没解决。满分的同学能否给点提示？谢谢！

BruteCollinearPoints.java和FastCollinearPoints.java里各一个错误，类型相同。

Test 10: Check that data type is immutable by testing whether each method
        returns the same value, regardless of any intervening operations
  *  input8.txt
     -  failed after 12 operations involving BruteCollinearPoints
     -  first and last call to segments() returned different arrays
     -  sequence of operations was:
          BruteCollinearPoints collinear = new BruteCollinearPoints(points);
          collinear.numberOfSegments() -> 2
          collinear.numberOfSegments() -> 2
          mutate points[] array that was passed to constructor
          mutate points[] array that was passed to constructor
          collinear.numberOfSegments() -> 2
          mutate points[] array that was passed to constructor
          collinear.segments()
          mutate array returned by last call to segments()
          collinear.numberOfSegments() -> 2
          collinear.numberOfSegments() -> 2
          collinear.segments()
     -  failed on trial 1 of 100

  *  equidistant.txt
     -  failed after 9 operations involving BruteCollinearPoints
     -  first and last call to segments() returned different arrays
     -  sequence of operations was:
          BruteCollinearPoints collinear = new BruteCollinearPoints(points);
          mutate points[] array that was passed to constructor
          collinear.segments()
          collinear.numberOfSegments() -> 4
          mutate points[] array that was passed to constructor
          mutate array returned by last call to segments()
          collinear.numberOfSegments() -> 4
          mutate points[] array that was passed to constructor
          collinear.segments()
     -  failed on trial 1 of 100

==> FAILED

Test 13: Check that data type is immutable by testing whether each method
         returns the same value, regardless of any intervening operations
  *  input8.txt
     -  failed after 10 operations involving FastCollinearPoints
     -  first and last call to segments() returned different arrays
     -  sequence of operations was:
          FastCollinearPoints collinear = new FastCollinearPoints(points);
          collinear.numberOfSegments() -> 2
          collinear.segments()
          mutate points[] array that was passed to constructor
          collinear.segments()
          mutate array returned by last call to segments()
          mutate points[] array that was passed to constructor
          mutate points[] array that was passed to constructor
          collinear.numberOfSegments() -> 2
          collinear.segments()
     -  failed on trial 1 of 100

  *  equidistant.txt
     -  failed after 11 operations involving FastCollinearPoints
     -  first and last call to segments() returned different arrays
     -  sequence of operations was:
          FastCollinearPoints collinear = new FastCollinearPoints(points);
          collinear.numberOfSegments() -> 4
          collinear.numberOfSegments() -> 4
          collinear.segments()
          mutate points[] array that was passed to constructor
          collinear.segments()
          collinear.numberOfSegments() -> 4
          collinear.numberOfSegments() -> 4
          collinear.numberOfSegments() -> 4
          mutate array returned by last call to segments()
          collinear.segments()
     -  failed on trial 1 of 100

==> FAILED



补充内容 (2017-2-28 20:15):
immutable的问题后来解决了。补发下了思路。请帖子内找。

先后提交了九遍，看了网上的提示才得了满分。。。心累

适当的使用Arrays.sort()非常有用！

交作业，

还是废了点时间的

请问，这个问题是啥问题？我程序里调用了point.toString()方法。。。
Test 8: Check for fragile dependence on return value of toString()
  *  filename = equidistant.txt
     -  student   solution has 1 non-null entries
     -  reference solution has 4 non-null entries
     -  3 missing entries in student solution, including: (30000, 0) -> (20000, 10000) -> (10000, 20000) -> (0, 30000)

  *  filename = input40.txt
     -  student   solution has 1 non-null entries
     -  reference solution has 4 non-null entries
     -  3 missing entries in student solution, including: (2000, 29000) -> (4000, 29000) -> (22000, 29000) -> (28000, 29000)

  *  filename = input48.txt
     -  student   solution has 1 non-null entries
     -  reference solution has 6 non-null entries
     -  5 missing entries in student solution, including: (1000, 26000) -> (9000, 26000) -> (11000, 26000) -> (18000, 26000)

==> FAILED

loveyomin 发表于 2016-9-25 21:01
请问，这个问题是啥问题？我程序里调用了point.toString()方法。。。
Test 8: Check for fragile dependen ...

就是没有找全所有的共线点

提交作业，没有满分的原因是改变了传入单数points，但是要用Arrays.sort 就会改变原点阵，除非重新建矩阵，但是这样多用了spacet

Raymomd 发表于 2016-9-26 02:47
提交作业，没有满分的原因是改变了传入单数points，但是要用Arrays.sort 就会改变原点阵，除非重新建矩阵， ...

effective java 里面建议 不要改变传入的参数，所以测试里才会有测试参数。。。points.clone()新建矩阵就好。空间满足题设要求，memory测试也是可以过的。。

Raymomd 发表于 2016-9-26 02:00
就是没有找全所有的共线点

嗯，错误提示是这个，但关键是，，，本机跑出来的结果是对的，比如第一个，他说student solution 1 non-null entries，但实际上我debug的结果就是4个。。。

loveyomin 发表于 2016-9-26 19:53
嗯，错误提示是这个，但关键是，，，本机跑出来的结果是对的，比如第一个，他说student solution 1 non-n ...

咦，你有testcode吗，哪里可以找到啊，我一开始和你有一样的问题，但后来发现还是没考虑所有情况