Code (C++ version)

Code (C++ version)

Code (Python version)

Code (C++ version)

Code (Python version)

Code (C++ version)

Code (C++ version)

Code (My stupid solution: C++ version)

Code (demon1999's fast solution: C++11 version)

UPD1: Note that the editorial of problem E is modified with some correction. Sorry for that inconvenience.

UPD2: The editorial is complete now. Hope you find it useful. :P

UPD3: It's seems that all bonus questions can be found in the comments. :) Don't hesitate to give them an upvote. :P