Yukon

Goal

Build up the four suits on the foundations, from Ace to King.

Setup

All 52 cards are dealt into seven columns: a single card in the first one, then one to six face-down cards topped by five face-up cards in the others. There is no stock and no draw pile.

How it works

• You place a card on a card of the next higher rank and of the opposite colour: a red 8 on a black 9.
• What makes Yukon special: any visible card can be moved, along with all the cards on top of it, even if they are not in order. Only the bottom card of the group has to fit its destination.
• An empty column accepts only a King (with whatever is on top of it).
• A face-down card is turned over as soon as it is uncovered.
• At the Diabolical level, the Russian rule applies: you build down in the same suit (an 8 of hearts only on the 9 of hearts). There is often only one path to victory.

Controls

• Drag and drop a card: everything on top of it follows.
• Tap a card: it goes to the best spot, the foundation first.
• Double-tap: straight to the foundation.
• Keyboard: Ctrl+Z to undo, I for a hint.
• As soon as all the cards are visible and in order, the game finishes by itself.

About the solver

Each deal is chosen by a solver that plays it with the cards face up, in a separate thread: depth-first search, ordered moves (uncover a hidden card, empty a column, repair a sequence), safe moves to the foundations, a transposition table and restarts with random variations. Difficulty is measured by the number of positions it has to examine. The hint and the “AI solves” button query the same solver on the current position (so it knows the hidden cards); a game finished by the AI does not count toward your records.