IOI/NOI/NOIP/ACM 練習場地

ZJU Online Judge: http://acm.zju.edu.cn/ 
PKU Online Judge: http://acm.pku.edu.cn/JudgeOnline/ 
Saratov State University Online Contester: http://acm.sgu.ru/
URAL Online Judge: http://acm.timus.ru/