Instead of checking all possibilities (like brute force), a constructive algorithm constructs the answer directly by following a specific logic or set of rules. Problem List: https://codeforces.com/problemset/problem/1353/C https://codeforces.com/problemset/problem/1353/D https://codeforces.com...
those who are preparing the problem sets are good coders (orange, red, ...), and they don't know what is the difficult point of easy problems (or do you still want to read "This is just a straightforward problem." for all the questions?)....