foo.cc: In function 'int main()':
foo.cc:11:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   11 |         for (int i=0;i<s.size();i++)
      |                      ~^~~~~~~~~
foo.cc:13:25: warning: array subscript has type 'char' [-Wchar-subscripts]
   13 |                 m[ s[i] ][1]++;
      |                         ^
foo.cc:14:29: warning: array subscript has type 'char' [-Wchar-subscripts]
   14 |                 if (m[ s[i] ][1] == 1)
      |                             ^
foo.cc:16:31: warning: array subscript has type 'char' [-Wchar-subscripts]
   16 |                         m[s[i]][0] = i;
      |                               ^

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