[Java] BST element distance - lowest common ancestor

So I was thinking about the parent pointer approach to find the distance between to elements in a binary search tree and avoiding using the path lists approach, which means finding the lowest common ancestor; that's the lowest node in the tree that is common to both paths to the two elements.
If the elements are one the child of the other, then it will be equal to the parent, otherwise it will either be the root if the elements are on completely different branches or the divergence node if the elements are in the same subtree.

Then I got down to coding and when I got to the LCA logic, finally, ... I did not use the parent pointer yet again :(

[Java] BST element distance - path lists

The exercise that stole too much time from me last time was about binary search trees. The description is quite simple: find the distance between two elements in a given tree; that means how many hops do you need to do to navigate to element B from element A; if the elements are the same, distance is 0, if one or both elements are missing, distance is -1.

[Java] Scorecard algorithm

Some time ago I took an online coding test which left me with an unfinished exercise; I played too long with the other one and had no time to finish this :(

However it seemed quite easy and interesting so I decided to finish it later, here is the description of the exercise as I remember it and my solution:

Bill plays some kind of game where the score is tracked on a scorecard; in addition to simple scoring moves, he can attempt (and possibly fail) more rewarding moves that will influence the score calculation.

Bill starts with a score of 0 and cannot earn negative points.

Bill can alter his total score by:

• scoring a point (integer) - it will be added to the total score
• doubling a previous score ("X") - the previous score will be doubled before adding it to the total score. If there is no previous score, it counts as 0
• summing two previous scores ("+") - the two precedent scores will be summed together before adding the result to the total score. If there are no predecessors, it counts as 0; if there is only one predecessor, it will be added again to the total score
• failing a move ("Z") - the previous score will be ignored from the total score and its value will also not be considered for subsequent special moves. If there is no previous score, this has no effects

[Oracle] Aurora module exception when compiling Java code on the DB

Sometimes it is possible to receive an exception when compiling Java code or running tools that generate Java code on the Oracle DB with this signature:

ORA-29516: Aurora assertion failure: Assertion failure at some_source:some_line_number

It is usually easy to prevent this error by disabling the JIT compilation on the DB:

alter session set java_jit_enabled = false;

Facebook and Airbnb login bug, now you are someone else

Well, everyone nowadays is running around trying to spot and fix bugs for money and I just stumble upon someone else's information for free.

This is an unexpected Christmas gift given it happened close to this huge fail from VISA, which makes it possible to guess full credit card details in a frighteningly fast amount of time. So read that article first, and then image what could someone do if they had all your personal info, including partial credit card data.

[Oracle] Initialise DB statistics to improve performance

A couple days ago we were analysing a customer issue concerning DB performance on simple and already optimised queries (indexes + hints).

Somehow, the customer had bad performance even after calculating statistics for tables and indexes. Turns out that everything was good except for the fact that Oracle can't imagine future statistics without some help; if a table is only filled after some time that the applications run, it is important to gather statistics again after the first initialisation.

It is also possible however to provide fake statistics immediately after the objects are created or modified so that the DB already has an idea of how the objects will look like and choose different query execution plans than the ones it would use for freshly created objects.

That's what the DBMS_STATS package and its EXPORT_ and IMPORT_ procedures are for.

[Oracle] List uploaded Java resources

After extending functionality on an Oracle DB with Java resources, it is possible to list the available ones and their status with a query on the user_objects table:

SELECT

  object_name

 ,object_type

 ,status

 ,timestamp

FROM

  user_objects

WHERE

  (    object_name NOT LIKE 'SYS_%' 

   AND object_name NOT LIKE 'CREATE$%' 

   AND object_name NOT LIKE 'JAVA$%' 

   AND object_name NOT LIKE 'LOADLOB%'

  ) 

AND object_type LIKE 'JAVA%'

ORDER BY

  object_type

 ,object_name

;