1.) Instead of using scanf() and printf() use
ios::sync_with_stdio(false); and cout/cin. Don`t use scanf() and printf()after writing ios::sync_with_stdio(false);, you will get incorrect output.
2.) Instead of writing vector<long long>::const_iterator cit;, write auto cit=[NameOfVector].cbegin().
3.) Never use std::list<>. They are only useful for large data types.
4.) Use #include <bits/stdc++.h> instead of writing each header file one-by-one. This only affects compile time. And compile time has nothing to do with competitive programming. Only running time matters!
5.) Use range-based for loops instead of writing full for loop for C++ Containers for accessing all values.
6.) Tired of remembering return type of functions. Use auto.
7.) Learn different functions available in <algorithm> library of C++. They are quite useful in places.
8) use different library like <limits> ex:-
<limits> gives much more insight about numeric types, such as whether they're signed, the number of base-10 digits they can handle, whether they can represent infinity or not-a-number sentinel values etc.
this all will reduce complexity which is helpful in execution of programs effectively
well for more library's