## Problem
https://oj.vnoi.info/problem/medquery
https://codeforces.com/problemset/problem/962/D
https://oj.vnoi.info/problem/colquery

## Tài liệu
https://www.youtube.com/watch?v=lQ0KTlXDRR0&t=2s
https://codelearn.io/Discussion/Topic/136961
https://cplusplus.com/reference/set/set/
https://cplusplus.com/reference/set/multiset/