Learn well block-cut

[bcs5]

It seems hard to do bridge and block-cut tree problems.
Problems:

• Bridge Tree
  • https://codeforces.com/contest/1000/problem/E
  • https://codeforces.com/contest/652/problem/E
• Block-cut:
  • https://codeforces.com/gym/102512/problem/A
  • https://www.codechef.com/problems/SADPAIRS
• Blogs
  • https://codeforces.com/blog/entry/68138
  • https://en.wikipedia.org/wiki/Biconnected_component