
New Cities
Sometimes damaged nodes are unrecoverable. In that case, people that were connected to the crushed node must migrate to another district while administration attempts to fix the node.
But if a crushed node disconnects multiple districts from one another, then the network splits into two sub-networks and every sub-network should have their own Mayor. And Mayors must use pigeons for mailing between each other. In that case, when the network is split you don’t need hundreds of pigeons.
Your mission is to figure out how many Mayors you need to control the entire city when some nodes are crushed. In other words, you need to figure out how many sub-networks will be formed after some nodes are crush and not recovered.

Input: Two arguments: the network structure (as a list of connections between the nodes) and the list of crashed nodes.
Output: Int. The amount of sub-networks formed after some nodes were crushed.
Example:
subnetworks([ ['A', 'B'], ['B', 'C'], ['C', 'D'] ], ['B']) == 2 subnetworks([ ['A', 'B'], ['A', 'C'], ['A', 'D'], ['D', 'F'] ], ['A']) == 3 subnetworks([ ['A', 'B'], ['B', 'C'], ['C', 'D'] ], ['C', 'D']) == 1
CheckiO Extensions allow you to use local files to solve missions. More info in a blog post.
In order to install CheckiO client you'll need installed Python (version at least 3.8)
Install CheckiO Client first:
pip3 install checkio_client
Configure your tool
checkio --domain=py config --key=
Sync solutions into your local folder
checkio sync
(in beta testing) Launch local server so your browser can use it and sync solution between local file end extension on the fly. (doesn't work for safari)
checkio serv -d
Alternatevly, you can install Chrome extension or FF addon
checkio install-plugin
checkio install-plugin --ff
checkio install-plugin --chromium
Read more here about other functionality that the checkio client provides. Feel free to submit an issue in case of any difficulties.