Four-Patch

Rules

Four-Patch is played on the same 4×4 grid as Crossed Corners, but it starts completely empty -- neither nor has a head start this time. Take turns filling in any open square.

Get 4 in a row -- a full row, column, or diagonal -- to win, same as before. But now a plain 2×2 block of your own color anywhere on the board wins too, so there are 19 different ways to win instead of 10: 10 lines plus 9 possible patches.

If all 16 squares fill with no winner, it's a draw. Who moves first alternates each new game.

Aggressive difficulty plays differently from the others: it only ever defends to stop your immediate win -- line or patch -- otherwise it ignores you completely and just pushes its own furthest-along threat. It's beatable in ways Hard isn't, but it won't hand you a win either.

One more thing worth knowing: Hard (and sometimes Medium) solves this board exactly rather than guessing, and the very first time it has to think through a mostly-empty board in a fresh browser tab, that can take a few seconds. Every move after that, for the rest of the session, is instant.

New to this one? Medium is a good place to start — it plays a tight, exact game except for the occasional careless opening move, so a win over a draw is well earned.

Controls

Columns are lettered a through d, left to right. Rows are numbered 1 through 4, counted from the bottom up (matching Four-in-a-Row's convention). The board starts completely empty -- every square is open on the first move.

With a mouse or touchscreen: click any open square to place your mark there.

With a keyboard: type a coordinate into the box below the board -- "b3," for example, is column b, row 3 -- then press Enter or Place.

Type status (or just the start of it, like "sta") and press Enter or Place at any time -- even when it isn't your turn -- to have the whole board read back to you.

Roots

Four-Patch is Crossed Corners' sibling — same 4×4 grid, same Tic-Tac-Toe and Gomoku lineage, but the board starts empty and a plain 2×2 block of your own color wins too, not just a full line. That second win shape was actually discovered by testing what happens if you bolt one onto Crossed Corners — see that game's own Learn More for the root of the line-based half.

Under the hood

Medium and Hard solve this one exactly too, but Four-Patch needs real machinery to get there where its sibling doesn't. Crossed Corners starts with 4 of its 16 cells already anchor-filled, leaving only 12 open — small enough for a plain memoized search. Four-Patch starts from a fully empty board with 19 win-groups (10 lines plus 9 possible 2×2 patches), a search big enough that a plain port of that same solver took roughly 10 seconds on the very first move, long enough to freeze the page. Getting that down to instant took three things layered together: real alpha-beta pruning, a transposition table keyed to the board's 8-fold rotational and mirror symmetry so equivalent positions are only ever solved once, and careful bookkeeping so a pruned, partial result never gets cached as if it were the exact answer — an earlier version skipped that last part and it silently broke hard-vs-hard's guaranteed draw. Medium and Hard both still lean on that exact solver for every move but one: each has a chance of playing something genuinely careless on its own opening move instead — Medium fairly often, Hard rarely — then exact play the rest of the way. It still always blocks an immediate loss; the point is a careless move, not a handed-over game.

Even with almost twice as many ways to win as a plain 4-in-a-row game, adding the 2×2 patches doesn't actually tip the balance: hard-vs-hard still always ends in a draw with perfect play on both sides, exactly like Crossed Corners. The patches just give both players another kind of threat to watch for along the way, not an easier path to victory.

Measured over real medium-vs-medium self-play, Four-Patch actually draws more often than Crossed Corners — 76% here versus 53% there — which can feel surprising mid-game, since a Four-Patch position usually still feels genuinely open when a Crossed Corners one has already gone quiet. That's the same size gap from above showing up again: Crossed Corners only has 12 open cells and 10 win-lines that all need to die before a draw is certain, so it tends to settle early. Four-Patch starts with nearly double that — 16 open cells and 19 win-groups — so even though more of its games end in a draw eventually, there's simply more board left alive for longer along the way before that becomes certain.

Aggressive plays the same way here as it does in Crossed Corners: no lookahead, take an immediate win if there is one, block an immediate loss if there is one, and otherwise greedily push whichever of your own still-live win-groups — line or patch — is furthest along. It ignores any group the opponent has already touched, so it won't waste a move extending a patch or line that can no longer be completed.