Five in a Row in a partially observable environment

X starts

Opponent

Board size

Percentage of hidden cells

20%

Cross-hatched cells are hidden — you can place there, but you won't see if the opponent has already taken the cell. If you play against the AI, the computer sees just as little as you do — it makes decisions under the same uncertainty.

Five in a row wins. After the game, all hidden cells are revealed.

Five in a Row in a partially observable environment

In regular five-in-a-row, both players see the whole board. But what happens if parts of the board are hidden?

Hidden cells – Cross-hatched cells are hidden. You can place your mark there, but you won't see what's underneath.

Blind moves – If you play on a hidden cell, you won't know whether the move succeeded. If the cell was already taken by your opponent, the move is lost — you lose your turn without having placed anything.

Five in a row wins – Same rules as usual. Whoever places 5 in a row first wins.

This is called partial observability — the agent only sees part of the environment's state. How does that affect your ability to make good decisions?