foo.cc: In function 'int cmp(std::__cxx11::string, std::__cxx11::string)':
foo.cc:19:20: warning: array subscript has type 'char' [-Wchar-subscripts]
         if (a[a1[i]]!=a[a2[i]]) return a[a1[i]]<a[a2[i]];
                    ^
foo.cc:19:30: warning: array subscript has type 'char' [-Wchar-subscripts]
         if (a[a1[i]]!=a[a2[i]]) return a[a1[i]]<a[a2[i]];
                              ^
foo.cc:19:47: warning: array subscript has type 'char' [-Wchar-subscripts]
         if (a[a1[i]]!=a[a2[i]]) return a[a1[i]]<a[a2[i]];
                                               ^
foo.cc:19:56: warning: array subscript has type 'char' [-Wchar-subscripts]
         if (a[a1[i]]!=a[a2[i]]) return a[a1[i]]<a[a2[i]];
                                                        ^
foo.cc: In function 'int main()':
foo.cc:25:34: warning: array subscript has type 'char' [-Wchar-subscripts]
     for (int i=0;i<26;i++) a[b[i]]=i;
                                  ^

自豪的采用jd5进行评测(github.com/masnn/jd5)