poj

POJ, or Peking University Online Judge, is a competitive programming platform and problem archive operated by Peking University. It provides an online judge that allows users to submit solutions in multiple programming languages and receive automated verdicts based on predefined test cases. The platform became a widely used resource for students, educators, and competitive programmers, hosting a large collection of algorithmic problems and supporting practice, contests, and learning.

Originally launched in the early 2000s, POJ helped popularize online judges in China and among international users. It features user accounts, problem indexing, sample input/output as provided in problem statements, and a ranking system that tracks user submissions and performance. Submissions are evaluated for correctness and efficiency, with verdicts such as Accepted, Wrong Answer, Time Limit Exceeded, and Runtime Error, along with runtime and memory usage feedback.

Over time, POJ's prominence has been surpassed by newer platforms with more features and more active communities, such as Codeforces, LeetCode, and AtCoder. Nonetheless, the site remains a historic and still-accessible archive, used by some learners and educators for practice and study. It is important to note that "POJ" can also be an abbreviation encountered in other computing contexts, though it is most commonly associated with the Peking University Online Judge; a related term, POJO, stands for Plain Old Java Object in software design, which is distinct from POJ.