IOM 2019, Блиц — Задача 75

OLYMPIAD OF METROPOLISES, Moscow, September 2, 2019 · 2 септември 2019 г.

Условие

Suppose there are $n$ guests at a meeting. It is known that every guest decided to present a gift to another guest in such way that every guest receives one gift. Find how many ways to present gifts are there if there are 7 guests. Two ways to present gifts are distinct if at least one guest gets a gift from a different guest.

Решение

---

Оригинал в Архива: blitz-en-all-task-final.pdf