foo.cc: In function 'int main()':
foo.cc:18:21: warning: array subscript has type 'char' [-Wchar-subscripts]
   18 |             cnt[s[j]] ++;
      |                     ^
foo.cc:19:25: warning: array subscript has type 'char' [-Wchar-subscripts]
   19 |             if (cnt[s[j]]>1)
      |                         ^
foo.cc:11:9: warning: variable 'start' set but not used [-Wunused-but-set-variable]
   11 |     int start=-1;
      |         ^~~~~

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