For an introduction to the game Blokus and puzzles based on
its use of sets of polyominoes (monominoes through pentominoes)
see my main Blokus Discoveries
Here we see another solution to the 18x20
The structure of the solution is shown as well, in two ways.
The small figure is a reproduction of the upper left quadrant
of the solution.
A representative of each type of piece is there.
(Creating such 9x10-1 configurations is a puzzle form in itself.
There are many. Note that each color conforms to Blokus rules.)
The skeletal figure, too, has one of each piece,
but these are all of the same color.
The overall solution
consists of four copies of either of these !
(It was constructed
from the quadrants. However, if you could create a 'snake' like
this, such that no two covered squares mirrored each other in
any quadrant, that would be another way.)
The quadrants are just rotated, reflected, and placed
next to each other. The skeletons are overlaid.
The same technique was used with a different 9x10 quadrant
to create a 19x19
solution. Here, only three colors were
used in each quadrant, so each color only appears in three
quadrants. The quadrants are 90° rotations of one another.
The same quadrant can be used to create an 18x20
The appearance becomes quite dramatic when the original
quadrant is reproduced in just three colors,
as shown on the right.