foo.cc: In function 'void create_tree(int)':
foo.cc:16:19: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   16 |  for(int i = 0; i < v[node].size(); i++)  //size函数求出node容器中的元素个数，即与node相邻的节点
      |                 ~~^~~~~~~~~~~~~~~~
foo.cc: In function 'void dfs(int)':
foo.cc:34:21: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   34 |    for(int j = 0; j < t[i].size(); j++)
      |                   ~~^~~~~~~~~~~~~
foo.cc: In function 'int main()':
foo.cc:83:9: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   83 |    scanf("%d%d",&a,&b);
      |    ~~~~~^~~~~~~~~~~~~~

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