2023 China TST, Day 1, Problem 2
Source:
March 14, 2023
combinatoricsChina TST
Problem Statement
people attend a party. There are no more than pairs of friends among them.
Two people shake hands if and only if they have at least common friend.
Given integer such that .
Prove that there exists a person , the number of people that shake hands with is no more than times of the number of ‘S friends.