Chu–Liu/Edmonds' algorithm

[indy256]

https://codeforces.com/blog/entry/20079
https://github.com/kth-competitive-programming/kactl/blob/master/content/graph/DirectedMST.h
https://en.wikipedia.org/wiki/Edmonds%27_algorithm
https://github.com/indy256/olymp-docs/blob/master/notebooks/teamnote.pdf
https://github.com/indy256/olymp-docs/blob/master/notebooks/codebook.pdf
http://neerc.ifmo.ru/wiki/index.php?title=Алгоритм_двух_китайцев