As I didn't find any blog regarding this. Let's discuss our approach here :)

Question A) Simple but tricky.

Question B) I used binary search on multiset to find the largest number <=2*ri.

Question C) My logic was to find the minimum index I (0<= I <=n) such that both sides should be a palindrome.

Question D) I thought to use some brute force and don't know why it passed partially.

Your approach will be welcome in the comment box. Thank you