Google and Facebook organize their own contests, I believe. And you can find problem repositories with judges that let you submit your solutions online. These a

Google and Facebook organize their own contests, I believe. And you can find problem repositories with judges that let you submit your solutions online. These are slightly tricky to use for learning, because they wouldn't tell you what went wrong with any particular solution. Some places, like topcoder and codejam, will post analyses of their contests that explain how to solve the problems. Topcoder also has many of these analyses going far back, so you can read them to learn about algorithm design. Links: http://www.topcoder.com/ https://code.google.com/codejam/ https://www.facebook.com/hackercup http://www.spoj.com/ http://uva.onlinejudge.org/