What are the resources with complex programming tasks?

Question

Programming

Good day.
I would like to improve my skill by solving complex problems.
I solved such problems as: the maximum product of three numbers in an array , the implementation of the Huffman algorithm , finding the index of the minimum value in the Binary Tree, combinatorics problems, etc.
He also solved problems from the Euler project . But there they specifically on mathematics.
You can throw in some difficult problems that are often given at interviews, or just interesting problems that take a lot of time to solve. And also, if possible, various resources with these puzzles (books, websites, articles, etc.).
PS: Preferably not specifically for mathematics (since there is an Euler site).
Thank you in advance.

Answer 1

Olympic programming. Here is a list of problems: https://icpc.baylor.edu/worldfinals/problems

Answer 2

freelance.ru
It took me half a year to solve one problem and it's still not ready for release. And I solved the other one in a day, but very hard work. So for every taste, and as close as possible to practice. Now think about it, I’m kidding, but I understand why reinvent the wheel when you can solve a variety of tasks on one site and also get money.

Answer 3

Olympic programming. For example, acm.timus.ru
But I still advise you to pay more attention to projectEuler. There are excellent programming tasks in the difficulty of 50-80.

Answer 4

codeforces.ru - Olympiad puzzles. You can decide, discuss with other people (both Russian-speaking and from all over the world) and watch other people's decisions