Knight leaving a castle by visiting its halls
Source:
April 19, 2013
Problem Statement
A castle has a number of halls and doors. Every door leads into another hall or outside. Every hall has at least two doors. A knight enters the castle. In any hall, he can choose any door for exit except the one he
just used to enter that hall. Find a strategy allowing the knight to get outside after visiting no more than halls (a hall is counted each time it is entered).