foo.cc: In member function 'int Solution::numIsland(std::vector<std::vector<char> >&)':
foo.cc:14:21: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::vector<char> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   14 |   for (int i = 0; i < grid.size(); i++)
      |                   ~~^~~~~~~~~~~~~
foo.cc:17:22: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   17 |    for (int j = 0; j < grid[i].size(); j++)
      |                    ~~^~~~~~~~~~~~~~~~
foo.cc:22:21: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::vector<char> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   22 |   for (int i = 0; i < grid.size(); i++)
      |                   ~~^~~~~~~~~~~~~
foo.cc:24:22: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   24 |    for (int j = 0; j < grid[i].size(); j++)
      |                    ~~^~~~~~~~~~~~~~~~
foo.cc: In member function 'void Solution::BFS(std::vector<std::vector<int> >&, std::vector<std::vector<char> >&, int, int)':
foo.cc:52:26: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::vector<int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   52 |     if (newx < 0 || newx >= mark.size() || newy < 0 || newy >= mark[newx].size())
      |                     ~~~~~^~~~~~~~~~~~~~
foo.cc:52:61: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   52 |     if (newx < 0 || newx >= mark.size() || newy < 0 || newy >= mark[newx].size())
      |                                                        ~~~~~^~~~~~~~~~~~~~~~~~~~

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