It is written in Java, but easy to extend to other languages, such as Python, C++. Just replace the Java syntactic sugar and advanced tricks, maybe just less concise.
With my limited time and ability, here only covers common data structure & algorithms. Almost suitable for interview, but insufficient for competition.
I have tried my best to collect and summarize the most general and best-practice templates in particular area, but this version may not be the best solution. Or, it's really the best performance and most concise solution, but it's not the suitable for you. Within acceptable performance, it is the best practice for you when you use it most conveniently.
Code templates is written by Java with some pseudo code, so I use self and add stub functions to pass compiler's check. You should replace them with your particular logic according to the comments. Who is this for? If you will have interviews soon, and plan to review data structure & algorithm. You can review by these summary, and improve practical skills by typical examples. If you want to study algorithm by practice, here you can understand the key point in templates, and practice the examples from easy to hard, to understand it deeper. If you are a LeetCoder, you want to focus on your weak topics, and have no idea to which problems to solve, here is well classified and provides the most typical examples. Or, you are too tired to find a fastest and elegant answer in discussion, here can save your time. If you are a Java beginner, and want to enhance your advanced Java skills, you can focus on Java tricks. Hope you will find useful and elegant techniques here.