One implementation of graph theory
Source: Indonesia Mathematics Olympiad 2008 Day 2 Problem 2
August 13, 2008
combinatorics proposedcombinatorics
Problem Statement
In a group of 21 persons, every two person communicate with different radio frequency. It's possible for two person to not communicate (means there's no frequency occupied to connect them). Only one frequency used by each couple, and it's unique for every couple. In every 3 persons, exactly two of them is not communicating to each other. Determine the maximum number of frequency required for this group. Explain your answer.