Solution

Note: the only change required to pass this level is this

---

Level 0

Usage

To submit your code, first commit, and then run git push.

Only the program input will vary; we'll always run against the same dictionary (test/harness will download that dictionary for you if you don't have it).

See https://stripe-ctf.com for context on this level.

Observations

It's hard to know what this script does, but it seems to take time depending on the size of the input:

$ time ./level0 < short.txt >/dev/null

real  0m1.231s
user  0m1.132s
sys   0m0.096s

Compare to:

$ time ./level0 < long.txt >/dev/null

real  0m14.060s
user  0m12.952s
sys   0m1.104s

wc -c shows that long.txt is about 10 times larger than short.txt, so it seems like the runtime grows linearly with input size. Since it also has to read the entire input, there's not going to be a way to do better than a linear-time solution.

Catalog

• build.sh: We'll run this file before trying to run your code. This is likely only relevant if you rewrite in another language, but it also could be useful for something like fetching dependencies via Bundler. Feel free to modify it arbitarily; we'll run the modified version on our build servers. (https://stripe-ctf.com/about#build has more information on the build process.)

• level0: The mysterious program. Why so slow?

• long.txt: An example long input file.

• short.txt: An example short input file.

• README.md: This file :).

• test/*: A framework to make it easy for you to run test cases locally. You should only ever have to run test/harness.