foo.cc: In function 'void tarjan(int, int)':
foo.cc:20:18: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   20 |     for(int i=0;i<v[u].size();++i)
      |                 ~^~~~~~~~~~~~
foo.cc:27:18: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   27 |     for(int i=0;i<b[u].size();++i)
      |                 ~^~~~~~~~~~~~
foo.cc: In function 'int main()':
foo.cc:50:13: warning: unused variable 'pre' [-Wunused-variable]
   50 |     int x=1,pre;
      |             ^~~
foo.cc:44:14: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   44 |         scanf("%d %d",&x,&y);
      |         ~~~~~^~~~~~~~~~~~~~~
foo.cc:62:14: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   62 |         scanf("%d %d",&xx[i],&yy[i]);
      |         ~~~~~^~~~~~~~~~~~~~~~~~~~~~~

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Found 6 testcases.
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