Explanation
Open the explanation (shows the answer)
The answer is b8. With best play to the end: +4 (a win by 4).
Best line: b8 a8 b5 a7 a5 g8 g1 a4 a2 a3
Other moves
| Move | Result | Why |
|---|---|---|
| g8 | -4 (a loss by 4) | g8 is in an even region (4 empties); b8 is in an odd one (3). The opponent's best answer is b3 (then a3 a8 a2). |
| a2 | -8 (a loss by 8) | a2 is in an even region (6 empties); b8 is in an odd one (3). Openness: 2 for this move (flips 1), 0 for b8 (flips 1). The opponent's best answer is a3 (then a4 a8 b5). |
| g1 | -10 (a loss by 10) | The opponent's best answer is a4 (then b8 b3 g8). |
| h7 | -10 (a loss by 10) | h7 is a C-square (next to the corner h8). In this shape it lets the corner be taken. h7 is in an even region (4 empties); b8 is in an odd one (3). The opponent's best answer is a8 (then b5 g7 h8). |
| g7 | -22 (a loss by 22) | g7 is an X-square (diagonal to the corner h8). While the corner is empty it tends to give the corner away. After this move the opponent can play the corner h8. g7 is in an even region (4 empties); b8 is in an odd one (3). The opponent's best answer is h8 (then h7 g8 b3). |
About these puzzles
Each position comes from a real game. The engine solved it to the end (perfect play by both sides) and only positions with a single best move, clearly better than the second-best move, were kept. "Best play wins by N" is the final disc margin when both sides play perfectly.
If you play a different move, you see the final margin your move leads to with perfect play afterwards, and how much it gave up. Results are stored only in this browser.
To be graded during a full game, go to the Reversi dojo.