Memory

Goal

Find the pairs of identical cards. The cards are laid face down; on each turn, you flip two. If they match, the pair is yours and you play again; otherwise, they are turned face down again.

Modes

• Against the AI: take turns; a mistake passes the turn. The player who finds the most pairs wins (a tie is possible).
• Solo: find all the pairs in as few moves as possible. The timer starts at the first card; your records (moves and time) are kept for each grid.

Grids

4 × 4 (8 pairs), 5 × 4 (10 pairs) or 6 × 6 (18 pairs), drawn at random from 24 designs: animals, heavenly bodies, fruit and symbols.

Controls

• Tap a card to flip it. On the keyboard: arrow keys to pick a card, Space or Enter to flip it.
• After a mistake, tap any card to flip the pair back without waiting.
• The Hint button points out a pair you have already seen, the twin you have already glimpsed of your card, or failing that a card that has never been flipped.

About the AI

The AI only sees the cards that are flipped over, exactly like you. Each card it glimpses is memorized with a probability that depends on the level, and may then be forgotten at every change of turn; at the lower levels, it also sometimes confuses the location of a card with that of a neighbour. At the Master level, its memory is perfect and its choices follow an optimal strategy computed by dynamic programming (analysis by Zwick and Paterson): it knows when to reveal a new card and when to flip a known card so as to teach you nothing. On a computer, the “AI memory” panel shows live which cards it remembers.