In a kingdom far far away, the King decided that the time
has come to find a husband for his princess daughter. The
King wanted to find a worthy lad for his princess, so he
promised to give his daughter away to the first young (or
old) man who would solve the puzzle that has stumped the
best of his court mathematicians for years. The puzzle is
very simple: in a palace, there are 25 rooms arranged in a
square--5 rows of rooms with 5 rooms in each row. In every
room there is a light switch which not only switches on/off
the light in that room, but also switches the lights in the
adjacent rooms--the room to the right, to the left, the
room above and the room below. Initially, all of the
lights are turned off. The goal is to turn the lights on
in every room of the palace.