Gaps

Gaps is a sliding puzzle wearing a card game's clothes. Four rows of thirteen, Aces discarded to leave four holes, and one rule: a hole takes the next card up in the same suit as whatever sits to its left. Fill all of them correctly and you end with four tidy suit runs.

It is also known as Addiction, Montana, Spaces and Vacancies, and the first of those is earned — the mechanic is unusually compulsive for something with so little to it. The cruelty is in the Kings: a gap that lands to the right of one can never be filled, so a careless move can quietly cost you a whole row. Three redeals keep it just about tractable.

The deck goes down in four rows of thirteen, then the Aces are pulled out and discarded — they take no further part. That leaves four gaps. A gap can only be filled by the card of the same suit ranked one above the card immediately to its left, so the row grows rightward as an ordered suit run. A gap at the start of a row wants a two. A gap sitting after a King can never be filled, because nothing outranks a King. You win when all 48 remaining cards form four complete suit sequences from two up to King. When you run out of moves, you may gather up everything not already in a correct run and redeal — three times.

Gaps after Kings are dead space, and creating one is the single worst thing you can do, so check what a move leaves behind before making it. The real currency is the leftmost positions: getting a two into the start of a row opens a run that can then extend all the way up. Since a redeal only gathers cards not already correctly placed, every card you lock into a valid run before redealing is a card you keep — so build correct runs early even if they feel slow. The article puts an experienced player at about 1 in 20 with shuffled redeals, improving to around 1 in 7 if the redeal preserves order.