Good Code might be a bit more popular than Spoj. We know about 1 link to it since March 2021 and only 1 link to Spoj. We are tracking product recommendations and mentions on various public social media platforms and blogs. They can help you identify which product is more popular and what people think of it.
Have you looked at spoj.com? It has a fair amount of different problems, some of them are pretty creative, you can take an inspiration from that. Source: about 3 years ago
Haven't tried this yet bit I have goodcode bookmarked. I think I discovered it via a subreddit before. Source: about 3 years ago
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