haxor | Educational virtual machine running custom assembly | Emulator library

This Hackerrank problem calls for a custom implementation of Merge Sort to keep track of inversions (swaps I think is a better way to refer to it.), but I am not able to capture the correct count for some data sets.

Blocked with a failing test case in my current implementation with a vector std::vector data { 7, 5, 3, 1 }; producing:

I have a form with a textbox, button and label. Some characters from the text in the textbox should be converted to numbers and some have to be converted to '/' and '|/|'. The last two are the problem i'm facing. I already tried using a @ before the '/' because i found that solution on stackoverflow but it doesn't work.

I need some basic validation (sanitation checks) to determine if some input is a valid SHA1 sum or just a (random) string. If possible with simple parsing rules or a Regex.

Are there any rules to what a SHA1 sum should adhere? I cannot find any, but from quick tests, all seem to be hexadecimal and around 40 characters long[1].

I am not interested in tests that prove whether or not the SHA-1 sum was made in a secure, properly random or other manner. Just that the format is correct.

I am also not interested in testing that the digest is an actual representation of some message; Just that it has the format of digest in the first place.

For the curious: this is for an application where I build avatars for users based on a.o. their uuid. I don't, however, want to place those uuids in the URL, but obfuscate them a little. So instead of avatars/baa4833d-b962-4ab1-87c5-283c9820eac4.png, we request avatars/5f2a13cb1d84a2e019842cdb8d0c8b03c9e1e414.png. Where 5f2a... is e.g. Digest::SHA1.hexdigest(uuid + "secrect").

On the receiving side, I am adding some basic protection that sends back a 400 bad request whenever something is obviously false. Such as avatars/haxor.png or avatars/traversal../../../../attempt.png. Note that this is a very much simplified example.

[1] Two tests with different outcome:

Using sha1sum on Ubuntu Linux: