Sphere Online Judge

Sphere Online Judge (SPOJ)
The Sphere Online Judge Problemset SPOJ is a programming site with a collection of selected but wide range of problems. It contains problems of all difficulties covering standard and non-standard algorithms. Moreover its problem set is increasing as one could post his/her own homemade problem. It also covers all the problems of the prestigious ACM International Collegiate Programming Contests(ICPC).

About
The SPOJ Project is developed and maintained by Sphere Research Labs, based in Gdynia, Poland .

Problems
SPOJ classifies problems into four categories - Classical, Challenge, Tutorial, and Partial problems. The classical problems work just like other online judges, where credit is given only on submitting an accepted solution.

Challenge proplems provide partial credit for submission (provided you meet a minimal threshold) but Tutorial and Partial do not contribute to the user's score.

Challenge problems are meant to challenge the user into completing the problem while abiding by secondary constraints. Problems are ranked based on how well you complete the problem, whether it's by obtaining the best result or through another metric. Tutorial and Partial problems act similarly are meant for the user to become familiar with a method of programming.

Unlike other online judges SPOJ does not organize problems in volumes by their index - they are normally referenced by their tag. However, this site will reference these problems by their numeric index.

Please use the Problem Template when adding new problems; see Help:Editing for a step-by-step guide.