We study a popular puzzle game known variously as Clickomania and Same Game.
Basically, a rectangular grid of blocks is initially colored with some number
of colors, and the player repeatedly removes a chosen connected monochromatic
group of at least two square blocks, and any blocks above it fall down.
We show that one-column puzzles can be solved, i.e., the maximum
possible number of blocks can be removed, in linear time for two colors, and
in polynomial time for an arbitrary number of colors.
On the other hand, deciding whether a puzzle is solvable
(all blocks can be removed) is NP-complete for
two columns and five colors, or five columns and three colors.