※ 引述《saladim (杀拉顶)》之铭言：
: 看书又看到卡住 请大家帮忙解惑阿~~~~
: 所看的书是 Algorithms in C++ by Robert Sedgwick, 第18章的DFS小节(18.4)
: 里面提到:
: We refer to a link from v to w in a DFS tree that represents a tree edge
: as :
: A tree link if w is unmarked
: A parent link if st[w] is v <