http://www.cnblogs.com/zhengyun_ustc/p/55solution2.html

http://www.cnblogs.com/zhengyun_ustc/p/55solution2.html

http://wenku.baidu.com/link?url=P756ZrmasJTKvzw9MJB5jwTreZjyCWzMJPY-_R9hOGPr3hYrLDv0QUCxl4mGrrpO-xUtcW3xCCTpsEurXVTeZ_vmzto_mgm8k78bXf4X8Qq

http://zhidao.baidu.com/link?url=WdFptJQBeuGYMVbqzZBCumZzTpkCLHg4nxLmLpUJ8qkdH9YzLxUkyUdJuHB4aVDlgVbeUbbdDdbhcSlN2QTsHK