Kata

The only performance tests are fixed, and they can be easily hardcoded allowing non-optimal solutions to pass.

Added random tests. Guess work solutions killed.

I think must be test case like [-5,-3,-2,-4,-1] equal 3

Approved

Typo in Java Sample test - wrong number params to prefix

assertEquals(PrefixPermutation.prefix(3, new int[]{2, 1, 3, 5, 4}));

Please, add details on the assumptions about the input array such as it containing only positive integers, without repetition, or add some tests.

Also precise input array could be large.

Could do with a performance tag.

My perfectly servicable solution chokes on 50000 element arrays.

To me the harder part to understand was how your example worked. May be a more detailled example would help other non-mathy-coders like me :

if given sequence is [2,1,3,5,4], then ...
  [2]         is a NOT a permuation of [1]
  [2,1]       IS a permutation of [1,2]
  [2,1,3]     IS a permutation of [1,2,3]
  [2,1,3,5]   is NOT a permutation of [1,2,3,4]
  [2,1,3,5,4] IS a permutation of [1,2,3,4,5]
  
...and there are 3 prefix permutations  

; ) )

Interesting one.

But you have to provide some fixed tests OF REASONABLE SIZE, in which you print the array to the console so that the warrior can debug is code. Currently, you use arrays that are too long to be displayed in the console. Note that you have to do the printing because if the warrior does it in his code, the big tests will be displayed too and that will provoque a failure.

There should be tests with numbers less than 1 and greater than length, like {-1, 4, 3, -99, 100}. Some solutions don't work in these cases.

And finally, needs random tests.

Expected and actual arguments in the test function are flipped.

Initial code is for placing code templates, not test descriptions.