Links

Local

Kattis, our own online judge.
DD2458 Programmering och problemlösning under press, a KTH-course for people interested in competitive programming.
KTH Challenge, our very own yearly competitive programming contest, usually held during the 2nd quarter of the year.
Nordic Collegiate Programming Contest is a contest for students in Nordic countries organized every year.
North Western European Regional Contest is an onsite qualification for ACM ICPC World Finals. KTH usually sends 3 teams based on their results in NCPC.

CodeForces, currently the most popular competitive programming website. It has online contests for individuals usually twice a week.
CSES, contains a large collection of competitive programming practice problems. There is an accompanying free handbook discussing all the tricks and algorithms used to solve the problems.
USACO Training Program is good for learning programming techniques. Especially recommended for beginners but more experienced will also find interesting problems here.
Sphere Online Judge has a large collection of problems. It is commonly used to test and benchmark implementations of algorithms.
Topcoder, one of the longest standing competitive programming websites. Here is a quick start guide.
UVa Online Judge has a huge problem archive and also runs ICPC style online contests.