1003 [K-th occurrence](http://acm.hdu.edu.cn/showproblem.php?pid=6704)
1002 [array](http://acm.hdu.edu.cn/showproblem.php?pid=6703)
1004 [path](http://acm.hdu.edu.cn/showproblem.php?pid=6705)
1005 [huntian oy](http://acm.hdu.edu.cn/showproblem.php?pid=6706)