commented because of being misinformed please ignore

No its in chinese. rock on!!

add me i am block.

you are absolutely right. you are my friend.

How about problems language?

For C: First you need to make everything integers. Do this by multiply everything with 100. Now, because dividing the notes by 2 is always better, let's just do that. --> Then the problem becomes, given a set of notes, check if you can use these notes to make certain sum (note that you can subtract). In math, this is check if an integer S can be represented as:

x₁ * c₁ + x₂ * c₂ + ...

for some constants c₁, c₂, ...

Now this is application of congruence equation, which to check if there is a solution, you just need to check if everything is divisible by gcd.

Edit: I mistakenly write solution for E here. (and get -10 :( )

For E: use inclusion exclusion principle and bitmask to iterate over all sets.

Let's create a set of interesting points. We add to this set start and end points. Also let's consider all pairs of towers. Let's look at intersection points of two circles with centers in this towers. If such point isn't covered by any other circle, we add it to our set.

Now for each pair of points in set we should find if we can go directly between them. So we just intersect this segment with all circles and look if all points in this segment is covered by at least one circle.

And now we can use dijkstra on this points to find a shortest distance.

P. S. I don't know how to prove that this algorithm works/works fast enough.

It is simpler than that ... It is just every edge in the tree acts like a bridge dividing the tree into to disconnected parts ... So the path from any node in the first part to any node in the second part will use that edge.