Competitive programming for beginners

Most of the answers here point out places where one can solve problems. I'm going to describe an approach to approaching ACM programming contests which is a bit different. My definition of an ACM beginner is someone who has not done an ACM regional contest before and has essentially no competitive programming experience, so I will try to cover more of the details from starting on working ACM problems to competing in a regional contest. First, get comfortable with one of C++ and Java. You're allowed to use C, C++, or Java - using C is more likely to hinder you in the long run, so get acquainted with one of the other two languages. You should be comfortable enough with the language that you can do some simple things. In particular, you should be comfortable with the following: Reading in data from standard input (the console), or from a file. You  must learn how to do this, since that's how interaction with the program is done. Basic arithmetic operations with integer num...

Please note that this answer is dedicated to competitive programmers only, as well as some recommendations in it. Competitive programming is not about readability, but about being able to code and debug fast.And still, the mains problems that I've seen: laziness and do not caring about code style even a little. That's ok if your program gets Accepted on first try, but otherwise you're gonna have a bad time debugging it. In general. So, mistakes (all of them are real stories): 1)Focusing on easier and 'cooler' things (like using of bitwise operations a lot instead of straightforward mathmatical formulas) instead of making code simpler to read and debug. Not only for them, but for the one who will help them too. 2)Copy-pasting it all around. "We don't need no architecture, just a little hack here is not bad. Oh, and here is another one. And here. C'mon, I still can tell you how is this supposed to work, but it doesn't work somewhy, can you help me?...