Hello,

I am working on this problem on Kattis. I have been constantly thinking about it for the last 3 hours, but it seems that I am totally hopeless on this problem. Can someone give me some hints?

(I know 3 hours is too short :(. Normally I would only give up if it lasted for a few days, but I am in my urgent self-training period before an NWERC, so I change my plan to solve problems that I am totally hopeless instead of those that are hard but still somehow solvable and I use all this time just to make sure that it is really impossible for me)

Thank you. Happy Coding

The answer is sum of the three sub-problems:

`?`

`?`

, no of inversions created against known charactersTo give you an example:

`01?01?`

`0101`

: 1 inversion x 2^k -> 4`??`

->`00`

,`01`

,`10`

,`11`

-> 1`?`

(consider both 0 and 1 cases) + Number of inversions created by the second`?`

.Thank you I have completed it and also understood it completely :)) You are a big help

hi, I have some detailed question about problem.

seperately within the whole string?

I'm probably just doing something wrong but could you explain how this would work with ?0?