foo.cc: In function 'int DFS(int)':
foo.cc:15:20: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   15 |  for (int i = 0; i < pic[num].size(); i++)
      |                  ~~^~~~~~~~~~~~~~~~~
foo.cc: At global scope:
foo.cc:28:1: error: '::main' must return 'int'
   28 | void main()
      | ^~~~

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