https://www.cnblogs.com/fenghaoran/p/dominator_tree.html
https://www.cnblogs.com/meowww/archive/2017/02/27/6475952.html
http://cogs.pro:8080/cogs/problem/problem.php?pid=vXSSzVkkW
支配树
原文：https://www.cnblogs.com/hjj1871984569/p/11267344.html
