Oust is a very unusual two player game, played on a hexagonally patterned board, usually around seven cells on a side. The board starts out empty. The two players, Red and Blue, take turns placing stones of their own color on unoccupied cells on the board. The goal is to completely clear the board of enemy stones, to “oust” your opponent – a paradox since the board is empty to begin with. Your opponent has to add at least one stone before you can capture all of his stones.
Normally an Oust board would be considerably larger than the tiny board used here in the diagrams. Draws cannot occur in Oust. Mark Steere designed Oust in July, 2007.
A non-capturing placement either forms no connections (adjacencies) with any stones, or forms one or more connections only with enemy stones. A non-capturing placement does not form any connections with stones of its own color. Making a non-capturing placement concludes your turn. In Figure 1 the only placements available to Red are non-capturing placements and are indicated by small red spots.
A “group” is a set of interconnected, like-colored stones. A group can be a “singleton” – a single stone which is not connected to any other stones of its color. A group includes all the stones of its own color connected to it.
When you place a stone which forms one or more connections with your own groups, you create a new, larger group of your own stones. You can only make such a placement if said new group will have one or more connections with enemy groups upon its creation and if all said enemy groups are smaller than said new group. Upon making such a placement, all said enemy groups are removed from the board.
In Figure 2, Red’s newly formed group of four captures the two blue groups it connects to.
In Figure 3, Red captures the two blue singletons connected to his newly formed group of five.
In Figure 4, Red’s newly formed group captures Blue’s group of four.
After capturing one or more enemy groups and while it is still your turn, you must continue to add stones until you make a non-capturing placement, at which time your turn is concluded.
If you have a placement available on your turn you must make one. If you don’t have any placements available you must pass your turn. There will always be a placement available to at least one of the two players. In Figure 5, it’s Red’s turn. He has no placements available and so must pass his turn.
You win by making a placement which captures all of the enemy stones on the board. In Figure 6, Red captures all of the blue stones and wins the game.
Feel free to publish this rule sheet, and to program the game of Oust for online or offline play. There is no licensing fee, and no royalties are expected. However please don’t change the name or the rules, and please attribute the game to me, Mark Steere. My other games can be found at marksteeregames.com.
Six computer levels. Level 1 places at random. Levels 2 and 3 mix random placements with sensible ones, level 2 mostly random and level 3 half and half. Level 4 always captures when it can and never seeds next to an enemy stone, but looks no further. Level 5 thinks ahead with a Monte Carlo search on most of its placements. Level 6, Unbeatable, searches for three seconds before every placement, with playouts guided by what it knows about safe seeds and safe captures. Levels 5 and 6 never miss a chain of captures that wins the game outright.
With Confirm placements on, a tap shows a translucent stone on the cell you tapped. Confirm places it, and so does a second tap on the stone. A tap on another legal cell moves the stone there. A tap anywhere else, on a placed stone, on an illegal cell, off the board, or on the Undo button, takes the stone back. With Confirm placements off, a tap places the stone at once.
The number of stones each player has on the board is shown above the board. When marking is on, a small spot marks each cell where you may place a stone (green on Red’s turn, yellow on Blue’s), and a ring around the spot marks a capturing placement. After a capture you keep placing until you make a placement that does not touch your own stones. If you have no placement available, the app passes for you. Undo takes back your last placement. Hint marks the placement that level 6 would make.