Olympiad problem about People. How to solve this problem?

Question

Programming

There are N people and integers A1, ..., AN; person i must be introduced to people ai. Can it be done?

Answer 1

I see that you have all the questions about the Olympiad problems, but it’s hard to answer them.
My advice is to take problems where you can find their analysis and / or see solutions, like on codeforces .
Here is the solution to this problem in python3:

xy = ({""}, {""})
for _ in range(int(input())):
    for i, t in enumerate(input().split()):
        xy[i].add(t)
print(max(map(len, xy)) // 2)