How to play
Reversi takes a minute to learn and a long time to play well. The board is 8 × 8. Four stones sit in the middle at the start, two black and two white on opposite diagonals, and black moves first.
A move is always a placement. You put one stone of your color on an empty square, and it has to sandwich at least one enemy stone: a straight, unbroken line of opponent stones running from your new stone to one of your existing stones. Lines can go across, up and down, or along either diagonal. Every enemy stone caught in such a line flips to your color, and one placement can flip lines in several directions at the same time.
If a square wouldn’t flip anything, you can’t play there. The squares that are legal for you right now are marked on the board, so you never have to hunt for them.
Passing and the end of the game
Sometimes a player has no legal square at all. Then that player passes and the other side moves again; the status line tells you when this happens. The game ends when neither side can move, which is usually when the board is full but can come earlier. The color with more stones on the board wins. An equal count is a draw.
Controls on the screen
- Opponent: Computer or Friend. Against the computer you are black and move first. Friend puts two people on one device.
- Difficulty: Easy, Medium or Hard against the computer.
- Hint points to a good square for the side to move.
- Undo takes back one move with a friend, or your move and the computer’s reply.
- New game resets the board.
The status line shows the count as “Black · White”. Flipped stones turn over with a short animation so you can see exactly what a move changed.
Strategy
The most common beginner idea is to flip as many stones as possible each turn. It feels good and usually loses. Here is what matters more.
- Corners can’t be flipped. No line can pass beyond a corner, so a stone there is permanent. Corners also anchor edges: stones you build along an edge from your corner tend to become permanent too.
- Stay off the squares touching an empty corner. The square diagonally next to a corner is the worst; it very often lets your opponent take the corner. The two edge squares beside a corner are risky for the same reason.
- Count your options, not your stones. In the middle game, the player with more legal moves has the upper hand. A quiet move that flips one interior stone and leaves your opponent few choices is often stronger than a big capture.
- Avoid building walls. A long run of your stones on the outside of the group gives your opponent many places to play against it. Stones in the interior are safer.
- Switch to counting near the end. In the last ten or so moves, positional ideas fade and the final total is what counts. Look for moves that flip long lines and for chances to force a pass.
About the computer
The computer uses a search with a board map that values corners highly and penalizes the squares next to them, plus a mobility count (how many moves each side has). With ten or fewer empty squares left it switches to pure stone counting. Easy looks one move ahead and allows itself some sloppy choices, Medium looks three moves ahead, and Hard searches deeper with a time budget so that it answers in about a second. In a 20-game test, Hard came out ahead of Medium and Medium ahead of Easy.
For a different kind of capture game, try Checkers; for a faster duel, Four in a Row.
If you enjoy Reversi, try Sea Battle or Snakes and Ladders next.
