Neighbouring coins on a chess board
Source: SAMO Senior Round 3 2013 Problem 5
September 17, 2013
combinatorics unsolvedcombinatorics
Problem Statement
Some coins are placed on a board. Two coins are called neighbours if they are in the same row or column and no other coins lie between them. What is the largest number of coins that can be placed on the board if no coin is allowed to have more than two neighbours?