growlnx's Listen To Your Heart

Author:
growlnx

Language:
C/C++

Upload:
2019-07-08 03:34

Download

Platform:
Unix/linux etc.

Difficulty:
2.5

Quality:
4.0

Arch:
x86-64

Downloads:
7

Writeups:
0

Comments:
9

Description

My girlfriend is a great programmer, she loves to study Complexity of Algorithms, Number Theory, Computational Geometry, Graphs, Dynamic Programming... But she hates sharing her codes. One day she showed me a program that, given a numerical sequence, showed a value in the output. I used my social engineering skills and managed to steal this executable, but I do not know how it works. Can you reimplement this algorithm?

Comments (9)
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paypain on 2019-07-16 11:18: sem nexo

k3rn3lP3nguin on 2019-08-20 02:00: Spent about an hour so far, there's not much at all said on this one so I suppose I'd find my current findings: binary expects args, lots of args. You can only use integers, and only count upwards. ./listen-to-your-heart 1 2 3 4 5 (result: 5) ./listen-to-your-heart 5 4 3 2 1 (result: 1) Found multiple user arguments in suspected main() Hopefully will find more patterns soon. Anyone else looking into this one?

Nim on 2019-08-20 15:04: I haven't even looked into the code yet, but I found a pattern. Of course, I'm not 100% sure I'm right, but I haven't been wrong for now. The program seems to count the numbers you input, but a number is ONLY counted if it's greater than a previous one. Example: ./listen-to-your-heart 1 2 3 4 5 returns 5, because 2 is greater than 1, 3 is greater than 2, 4 is greater than 3 and 5 is greater than 4, so the counter is incremented 5 times. But, if we run this: ./listen-to-your-heart 34 36 35 37 that returns 3, because: -the counter is initialised at 1 (with the input 34) - +1, because 3634 - +0, because 35 is not greater than 36 - +1, because 3736 I tested this with multiple inputs, of different values, and it worked each time. So if I had to quickly rewrite the algorithm: -------------- inputs = list of inputs max = inputs[0] counter = 1 for i in inputs: if i not an integer: display "Only Integers!" exit if imax: max = i counter += 1 display counter exit ------------------------

Nim on 2019-08-20 15:06: (shit, the greater and lesser signs disappeared in my previous comment, and the spaces for indentation too... It's the first time I comment on this website, sorry. I hope it's still clear tho)

growlnx on 2019-09-19 03:21: Hint: There is a great possibility that this program is implementing a classic algorithm.

E13V3N on 2019-11-29 10:56: Did you manipulate the longest increasing subsequence algorithm? It seems like, its counting longest increasing subsequence but in some test cases, it's not giving the longest subsequence length.

vr0n on 2020-03-05 17:08: Anyone got a solve on this one? I've done most of the level 1 chals, but can't seem to get this one.

mistilteinn on 2020-05-22 13:33: author's hint and a bit of playing around allows you to implement the algorithm without static analysis of the actual code

growlnx on 2020-06-01 00:19: its counting longest increasing subsequence but in some test cases, it's not giving the longest subsequence length. Hey @E13V3N, could you give to us a more detailed example of these test cases? I would like to apologize for the delay in answering your question.

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growlnx's Listen To Your Heart