I'm still puzzled how the Fulfillment[1] game builds a board by doing the opposite of this. Naively adding random walls clearly doesn't lead to a board filled w

I'm still puzzled how the Fulfillment[1] game builds a board by doing the opposite of this. Naively adding random walls clearly doesn't lead to a board filled with tetris pieces. [1] http://homokaasu.org/gasgames/game.gas?27 http://homokaasu.org/gasgames/game.gas?27