O An Quan

Goal

Ô ăn quan (“mandarin square capturing”) is a traditional Vietnamese children’s game, once played with a board drawn in the dirt and a handful of pebbles. The board has 2 rows × 5 citizen pits, with a half-moon mandarin pit at each end. At the start each citizen pit holds 5 stones and each mandarin pit holds one big mandarin stone. A small stone is worth 1 point, a mandarin 10 points. Whoever has more points at the end wins. You (or Player 1) own the bottom row; the AI (or Player 2) owns the top row.

How a turn works

• Pick one of your own citizen pits that has stones, then pick a direction (left or right). You can’t pick a mandarin pit, an empty pit or an opponent’s pit.
• Take all the stones and drop them one by one into the following pits in that direction. Sowing goes all the way around the board, through the mandarin pits and the opponent’s row.
• Keep sowing: after the last stone, if the next pit is a citizen pit with stones, pick them all up and keep sowing in the same direction.
• Capture: if the next pit is empty and the one after it has stones (or a mandarin), you capture that pit into your store.
• Chain captures: after a capture, if there is again one empty pit followed by a pit with stones, capture again — and so on.
• Turn over: when the next pit is a mandarin pit that still holds something, or when you meet two empty pits in a row.

Examples

• You pick a pit with 3 stones and sow right: the next 3 pits get one stone each. If the 4th pit holds 6 stones, you pick them up and keep going.
• The last stone lands, the next pit is empty and the one after has 4 stones → “Captured 4 stones!”. If after that there is another empty pit and then a mandarin pit with the mandarin and 2 stones → you also take 10 + 2 = 12 points.
• The last stone lands right before a mandarin pit that still has its mandarin → your turn is over; you never pick up a mandarin pit.

Empty row and borrowing

If all 5 of your pits are empty when your turn starts, you must take 5 stones from your store and put one in each pit. A captured mandarin can be exchanged for 10 stones. If your store has fewer than 5 stones, you borrow the rest from your opponent (shown as “owes” next to the store) and pay it back at the end. If neither side has enough, the game ends immediately.

End of the game

When both mandarin pits are completely empty (mandarin and stones captured), the game ends. Each player collects the stones left on their own row, debts are repaid and points are counted. Example: you have 1 mandarin + 23 stones, collect 4 more from your row and owe the AI 2 → 10 + 23 + 4 − 2 = 35 points.

Young mandarin rule (optional, off by default)

When enabled, during the first 10 moves (5 per player) a mandarin pit that still has its mandarin but fewer than 5 small stones is “young” and can’t be captured — the turn simply ends. Toggling the rule starts a new game.

Controls

• Computer: click a highlighted pit on your row; two arrows ◀ ▶ appear next to it — click one to sow. Keyboard: ←/→ pick a pit, Z sow left, X sow right, Esc to cancel.
• Phone: tap one of your pits, then tap the big ◀ or ▶ arrow under it.
• Choose Vs computer (Easy / Medium / Hard) or 2 players on one device; Player 2 owns the top row. Changing mode starts a new game; difficulty changes apply right away.
• The sowing animation can be normal, fast or off. ⏩ Skip finishes the current move instantly.

Tips

• Before sowing, count where the last stone lands and what comes after it — that’s the whole secret.
• Capturing a mandarin early is worth a lot, but don’t empty your own row or you’ll have to spend stores to refill it.
• Avoid leaving “one empty pit then a big pit” in your opponent’s path.