foo.cc: In function 'size_t dfs(const std::string&)':
foo.cc:28:22: warning: comparison of integer expressions of different signedness: 'size_t' {aka 'long unsigned int'} and 'int' [-Wsign-compare]
   28 | for (size_t j = 1; j <= n; j++) {
      |                    ~~^~~~

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