Uva Online Judge

Another Online Judge.

Why are they important?
I think, experience and practice is really important in this area of science as it is in all the rest.
Vasyl Biletsky, gold prize winner, ACM World Finals 2009, thinks so. When I asked him about the most important part of his education, he replied immediately: "Practice, Start with easy questions and continue with harder ones."

Universidad de Valladolid is the owner. Uva Online Judge is different from the other judges because it provides problem sets in groups:

Problem Set Volumes 
Random problems. Total submissions, succesful submissions, total users, successful users statistics for each problem can be seen.

Contest Volumes 
Problems from different contests. Same statistical information is shown. Best place to prepare for the contest that you want to join.

Prominent Problemsetters
Problems set by 23 diferent problemsetters. If you are a fan of one of them, you'll love it.

ACM-ICPC World Finals
1990-2000 ACM ICPC World Finals Problems.

Programming Challenges (Skiena&Revilla)
Challenges. 14 Chapters.

AOAPC I: Beginning Algorithms Contests(Rujia Lui) 
If you are a newbie, then here is for you. Volumes are:
Volume 0. Getting Started
Volume 1. Elementary Problem Solving
Volume 2. Data Structures
Volume 3. Brute Force
Volume 4. Algorithm Design
Volume 5. Dynamic Programming
Volume 6. Mathematical Concepts and Methods
 Volume 7. Graph Algorithms and Implementation Techniques

Competitive Programming: Increasing the Lower Bound of Programming Contests (Steven & Felix Halim) 
Chapter 1. Introduction
Chapter 2. Data Structures and Libraries
Chapter 3. Problem Solving Paradigms
Chapter 4. Graph
Chapter 5. Mathematics
Chapter 6. String Processing
Chapter 7. (Computational) Geometry

In their own words:

"Here you will find hundreds of problems. They are like the ones used during programming contests, and are available in HTML and PDF formats. You can submit your sources in a variety of languages, trying to solve any of the problems available in our database."

Uva Online Judge
http://uva.onlinejudge.org/