As I mentioned in my post introducing Project 462, I have spent some time in the past working on historical CodeForces problems to get some idea of what their programming competitions are like. I thought it would be interesting to go through one of those problems, Hot Bath, from the perspective of a CodeForces beginner. In CodeForces Beta Round #93, Hot Bath was Problem C in the Division 2 contest, and Problem A in the Division 1 contest. In the CodeForces system, that means the problem is targeted at Division 1 (more experienced) contestants who are just getting their fingers warmed up at the beginning of a contest, and at Division 2 (less experienced) contestants who have finished a couple of easier problems, and are ready for something that requires more thinking. Based on the information in the standings report for that round, several top Division 1 contestants submitted an accepted solution in about ten minutes, so we can take that as a reasonable lower bound.

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The Story So Far

Long ago (2008), I read a post on the “xkcd blag” (yes, Randall Munroe occasionally just writes regular blog posts) about “a site with a lot of math-oriented programming problems that you can solve in any language.” I like math and programming, so that seemed like fun. I spent a few years on and off working through the first 76 problems on Project Euler, at which point the problems started to require more math than I had at my disposal. Around that time (2011), I heard about a site called CodeEval that was coming out of beta. CodeEval also has programming puzzles, but with less of a math emphasis. As I’m writing this post (early 2015), I have finished 107 puzzles on CodeEval. Back in 2011, a site called CoderCharts (no longer online) was briefly popular. CoderCharts hosted contests that ran over several days, like the long contests on CodeChef. That was my first experience with contests that allowed participants to compete against each other during an event. However, the schedule allowed a day or so for each problem, so there was plenty of time to think.

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In my deliberate practice plan for software developers, I suggested that aspiring programming experts find a source of programming problems to use as part of a deliberate practice routine. It turns out that there are more pre-packaged programming problems out there than you could get through in a lifetime. Many of them come from the world of competitive programming. Competitive programming is a “mind sport” like a quiz show or a chess tournament. Contestants are given a set of programming problems, and they have to write programs to solve them. In most cases, programs are submitted to an online judge, which verifies that they produce the correct answer and don’t run longer than a specified time limit. Participants are scored according to how quickly they submit a correct and sufficiently fast program. They may also have a chance to submit challenges to try to stump their colleagues’ programs. Competitive programming is most popular among high school and college students outside of the United States, but there are plenty of competitive programmers who don’t fit that profile. For a colorful description of one contest, the 2010 International Olympiad in Informatics, see the Wired article Teen Mathletes Do Battle at Algorithm Olympics. Regular online contests take place at TopCoder, CodeChef, and Codeforces. These sites also provide access to past problems, which can be used for practice.

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