1、http://www.spoj.pl/problems/AIBOHP/：ｄｐ
2、http://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&category=114&page=show_problem&problem=615
3、http://acm.hdu.edu.cn/showproblem.php?pid=3639
