As a follow up to my previous blog-post, I've created a vectorized version of the CodeForces logo. You can download it in SVG format here: link. Also, here it is rendered at 2308x500 resolution: another link.

Edit: Another version, hand-crafted using the Copperplate Gothic font. You can download it here in SVG format: link, and a high-res rendered version: another link.

Hope this will be of interest!

What are the conditions for one to be eligible to submit a problemset for a CodeForces round? Is there a minimum rating limit? And what's the exact way of proposing a set?

Thanks.

Hi, I've noticed that the CodeForces logo is currently only available to the public in a low resolution version. Can the admins (or whoever designed the logo) provide a version rendered at a higher resolution? I imagine this would be of interest to some people.

(I know such requests shouldn't be posted in blogs, but I thought this would potentially get more attention than otherwise).

Thanks a lot in advance!

Hi! Although you might not want to hear from someone with such a rating, well, give me a chance, I hope I do better in upcoming rounds :D
1) The 250-point problem: ( Link )
In this problem, the main thing to notice is that the sequence is either of the form "xo" or "ox" repeated n / 2 times. Thus, we can test the known letters and see which type they match, and print the one that matches.
2) The 500-point problem: ( Link )
Here, the most important note is that if x XOR y = z then y = x XOR z. So, we can try all pairs of a plaintext XOR a ciphertext to be key, then check if it's valid. A key is considered valid if, for every ciphertext, there exists a plaintext which when encrypted using the current key gives this same ciphertext.
3) The 1000-point problem: ( Link )
First, you need to read the statement carefully, as it clearly states that the characters in the original message are distinct, and thus the characters in each subsequence are distinct. Now, we can consider the given subsequences as "letter x is before y" relations and put those as edges in a graph. Note that if you're given a subsequence x_1, x₂, ..., x_n, then for each i, x_i comes before all x_j : i < j <= n. Now that we have the graph, all we have to do is a topological sort. Since we're being asked for the lexicographically minimum string, among the zero-in-degree nodes, we choose the one that corresponds to the lexicographically minimum character.
I hope the explanations were clear, if you notice anything wrong or vague, please tell me :D