foo.cc: In function 'int dfs(std::vector<std::vector<int> >&, int, int, std::vector<std::vector<int> >&)':
foo.cc:6:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     if(matrix.empty()||ph>matrix.size()||px>matrix[0].size())
                        ~~^~~~~~~~~~~~~~
foo.cc:6:44: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     if(matrix.empty()||ph>matrix.size()||px>matrix[0].size())
                                          ~~^~~~~~~~~~~~~~~~~

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