But you, my avid reader, protest “it’s a test to see how you think and reason”. Okay that’s fair, but I, for the sake of discussion, claim quicksort and other standard algorithms aren’t the right way to test an applicant’s reasoning ability. All applicants know quicksort could be asked, so we all look it up. Now, when we are sitting down during an interview, we’re trying to recall all the intricacies of a mature algorithm. Instead of reasoning through divide-and-conquer, I’m thinking “oh crap, now how to I pick the pivot to avoid those QS-attacks?”. I’m trying to remember how to get all the details right, when I should be iteratively addressing problems as they arrive.

Of course, if you’re hiring someone to squeeze out the next 1% of execution time in some DB-query, then absolutely he or she should know every damn intricacy of the standard algorithms. But for the rest of us, I think non-standard brain teasers or puzzles seem much better than reproducing a well-known mature algorithm.

IMHO =)

XKCD always getting to the heart of the matter

The trick here is to get ROOT to echo all the TBranch names to stdout (through TTree::Print()) so that we can use all our normal grep tricks to find that one name we are looking for.  Here is the script in its totality:

#!/bin/bash
#./thisScript treeName fileName
{ echo "TFile f(\"$2\", \"READ\")" ; echo "$1->Print()" ; echo ".q" ; } |\
 root -l -b |\
 grep -v "^[*]Tree" |\
 sed -n -r "s/^[^:]*:([^ ]+)\s+:.*/\1/p"
#EOF

Bash curly braces always freak me out, because they can do several different jobs. In this particular case, we are moving the output of several commands to stdin of another process. Remember in the above script, the $1 and $2 get expanded to the first and second arguments passed to the shell script. Here is, effectively, how the curly braces and ROOT call are interacting…

$> root -l -b
##ROOT ASCII ART###
>>>TFile f("$2", "READ")
>>>$1->Print()
>>>.q
$>

Which causes ROOT to vomit lots of text like this…

...
*Entries : 172375 : Total Size= 23966439 bytes File Size = 13664685 *
*Baskets : 917 : Basket Size= 32000 bytes Compression= 1.75 *
*............................................................................*
*Br 180 :mooreseg_phi : vector<double> *
*Entries : 172375 : Total Size= 23968281 bytes File Size = 8502181 *
*Baskets : 917 : Basket Size= 32000 bytes Compression= 2.82 *
*............................................................................*
*Br 181 :mooreseg_theta : vector<double> *
*Entries : 172375 : Total Size= 23970123 bytes File Size = 14002768 *
*Baskets : 917 : Basket Size= 32000 bytes Compression= 1.71 *
*............................................................................*
...

Since all that goes to stdout we can just grep/sed our way through it until we get a pretty list of branch names.  Now we just have a plain text stream.

$>./treeprint.sh CollectionTree data12_jte.root
...
mooreseg_z
mooreseg_phi
mooreseg_theta
...
$>

Pretty simple huh? How about that for “worse is better”?