Wrong Answer
/in/foo.cc: In function 'void dfs(int)':
/in/foo.cc:17:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
for (int i = 0; i < a[x].size(); i++) //走不下去就是叶子结点
~~^~~~~~~~~~~~~
/in/foo.cc: In function 'void dfs(int)':
/in/foo.cc:17:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
for (int i = 0; i < a[x].size(); i++) //走不下去就是叶子结点
~~^~~~~~~~~~~~~
