foo.cc: In function 'int* get_next(std::__cxx11::string)':
foo.cc:10:12: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     while(i<s.length()-1)
           ~^~~~~~~~~~~~~
foo.cc: In function 'int KMP(std::__cxx11::string, std::__cxx11::string)':
foo.cc:40:9: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     if(j==t.length())
        ~^~~~~~~~~~~~

自豪的采用jd5进行评测(github.com/masnn/jd5)