Master Parity in Reversi to Boost Your Endgame Win Rate
Published
Once you learn the basic rules of Reversi and get used to preserving discs in the midgame, you may struggle to maximize your disc count at the finish. An essential concept that decides endgame victory is parity in Reversi. Understanding how it works lets you calmly find winning lines even in smartphone matches.
Basics of Parity: Odd Regions and Even Regions
In the endgame, empty squares divide into several isolated regions along the edges of the board. Parity is a tactic focused on counting the empty squares in each region so that you can play the last move in that region.
When a region has an even number of empty squares, your opponent playing first allows you to make the final move. Conversely, if your opponent enters an odd region first, they claim the last move. Playing the last move lets you secure stable discs in that region, significantly boosting your final count.
- Odd region (1 empty square, 3 empty squares, etc.): Play here first yourself, aiming to claim the final move in the region.
- Even region (2 empty squares, 4 empty squares, etc.): Avoid playing here first; let your opponent enter so you take the final move.
Figure 1 as text
Black discs (28): f1 d2 d3 e3 f3 c4 d4 f4 c5 f5 g5 h5 b6 f6 g6 h6 a7 b7 c7 d7 e7 f7 g7 h7 e8 f8 g8 h8
White discs (29): a1 b1 c1 d1 e1 a2 b2 c2 e2 f2 a3 b3 c3 g3 h3 a4 b4 e4 g4 h4 a5 b5 d5 e5 a6 c6 d6 e6 d8
To move: White
Empty regions: a8 b8 c8 (3 squares, odd), g1 h1 g2 h2 (4 squares, even)
Board (from rank 1): WWWWWB../WWWBWW../WWWBBBWW/WWBBWBWW/WWBWWBBB/WBWWWBBB/BBBBBBBB/...WBBBB
In this diagram, the remaining empty squares split into 2 areas: an odd region of 3 at a8, b8, and c8, and an even region of 4 at g1, h1, g2, and h2. By playing into the odd region first, White on turn can secure the final move in that region.
Midgame Preparation and the Role of Openings
To use parity effectively in the endgame, your play up through the midgame is vital. In the opening phase, there are book openings such as the Rabbit, Tiger, and Cow, all aimed at minimizing the discs flipped in the opening phase and midgame while reducing squares available to your opponent.
Maintaining many options prevents situations where you are forced into an even region in the endgame. In addition, avoiding careless moves into X-squares or C-squares and keeping corners out of enemy hands helps secure endgame initiative.
Play in the app
Putting these concepts into practice on the board is the fastest way to learn. Play to the end against an on-device AI even without an internet connection.
Summary of Endgame Move Decisions
When reaching the endgame, count the empty squares in each region across the board to choose your move.
Figure 2 as text
Black discs (31): e1 f1 g1 h1 a2 b2 e2 f2 g2 a3 b3 d3 f3 a4 h4 a5 d5 g5 h5 a6 b6 f6 g6 h6 a7 b7 g7 h7 a8 g8 h8
White discs (30): c1 c2 d2 h2 c3 e3 g3 h3 b4 c4 d4 e4 f4 g4 b5 c5 e5 f5 c6 d6 e6 c7 d7 e7 f7 b8 c8 d8 e8 f8
To move: Black
Empty regions: d1 (1 squares, odd), a1 b1 (2 squares, even)
Board (from rank 1): ..W.BBBB/BBWWBBBW/BBWBWBWW/BWWWWWWB/BWWBWWBB/BBWWWBBB/BBWWWWBB/BWWWWWBB
| Region Status | Turn Decision | Objective |
|---|---|---|
| Odd region | Play first yourself | Leave an even region for the opponent and play the last move |
| Even region | Do not play first yourself | Let the opponent play first and play the last move |
Practice with Smartphone AI Matches
Once you master the theory, practice counting empty squares in actual play. The smartphone Reversi app Patent War lets you play against an on-device AI for free. You can also review your endgame moves with its free AI analysis, making it ideal for practicing parity.
Carefully placing each disc while staying aware of endgame counts leads to consistent victories.
Frequently asked questions
What is parity?
It is the strategy of ensuring you play the final move in isolated empty regions during the endgame. Playing the last move makes it easier to flip discs heavily and convert them into stable discs.
Why shouldn't you enter an even region first?
Because playing into an even region first allows your opponent to play the final move. Forcing your opponent to play first guarantees you secure the last move in that region.
What causes parity to fail?
It breaks down when your mobility is restricted in the midgame, forcing you into undesirable even regions. You must limit flipped discs from the opening phase to keep options open.
Can I practice with the Reversi app Patent War?
Yes, you can play offline against an on-device AI and review endgame moves for free. You can play without data and verify your moves using post-match AI evaluations.
Play in the app
Explore a steampunk world with the Reversi app Patent War. Start your journey and play against AI for free.