Can you solve this puzzle involving regular expressions?

  • #1
MesonMarcus
2
0
can anyone help solve this puzzle regarding regular expressions? I was given this in an interview test from BAE systems cyber security department a few years ago and just came across it again, still haven't managed to get anywhere like an answer. I have tried matching each line of regex to form words but no look. The puzzle is as follows:
unnamed.png


.{14}security.{15}
[^s]{3}s [^s]{6}s[^s] s[^s]{12}s [^s]{8}
def
^It'..[ywkni][klmop][zwta]
ce.$
jus
[^f]*fenc
y, it's
t ...t

Give your answer.

This is the best I could get...

...security...
bees xxxxxxsx sxxxxxxxxxxxxs xxxxxxxx
def
It's not
ce.
jus
xfenc
y, it's
t xxxt

but makes no sense...
 

Answers and Replies

  • #2
14,194
8,183
The idea is to find a line that matches each of the regex strings.

[^x] means doesn’t match x and

{99} is the number of times to match with * for 0 or more and + for one or more.

^ outside of the [ ] means beginning of the string and $ means the end of the string.

I think the first line matches a string containing the text security

. . . . . . . . . . . . . . s e c u r i t y . . . . . . . . . . . . . . .

the second line matches a line where the 4th character is an s and some more s later on.

I t ‘ s . n o t . . . . . . s e c u r i t y . . . . . . . . . . . . c e .

my attempt yielded the sentence but it doesn’t match all the criteria.

I T ' S _ N O T _ J U S T _ S E C U R I T Y , _ I T ' S _ D E F E N C E .
 
  • #3
MesonMarcus
2
0
awesome!
 
  • #4
pbuk
Science Advisor
Homework Helper
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I T ' S _ N O T _ J U S T _ S E C U R I T Y , _ I T ' S _ D E F E N C E .
It's not just security, it's defence. works for me.
 
  • #5
14,194
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I had trouble with line 2 aka the s not s expression. It seemed not all the ‘s’ characters lined up in my solution although I didn’t test it.

I ll have to try it in AWK, my favorite go to language.
 
  • #6
pbuk
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I had trouble with line 2 aka the s not s expression. It seemed not all the ‘s’ characters lined up in my solution although I didn’t test it.
Line 2 only depends on 's's and spaces in the right place. It won't match if you use the US spelling for defence, unsurprisingly given the employer :biggrin:
 
  • #7
14,194
8,183
But it seemed solving it on paper that a couple of s characters were off According to that regex. I chalked it up to the possibility that the expression was an outlier perhaps designed to be misleading ala obfuscation Aka security thru obscurity.

I as puzzled by the defence spelling too but decided that since BAE is a British company that the spelling was correct. I imagine that would have tripped up a few Americans applying for the job. :-)
 

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