Connect Four

The board, and how you win

The grid is 7 columns wide and 6 rows deep — 42 cells. You and the CPU take turns dropping one disc at a time, and a disc never stays where you point: it falls to the lowest free space in the column you chose.

You win the moment 4 of your discs stand in a line — up a column, along a row, or on either diagonal. The CPU wins the same way. If all 42 cells fill and neither side has made four, the match is a draw.

• Discs carry no letters and no numbers. Yours is the title’s own colour and the CPU’s is this game’s second colour, so the board reads identically in every language.
• The winning four is ringed and every other disc is dimmed, so the result never rests on colour alone.
• The last disc dropped carries a small mark. It is how you find the CPU’s move without having to watch for it.

There is no score in this game and no clock on the screen. A match is a win, a loss or a draw, and your time is recorded quietly for the statistics only.

Dropping a disc

A move is a column, so a column is what you press: the board is 7 tall buttons rather than 42 separate cells.

• Tap anywhere in a column and your disc falls to the lowest free space in it.
• A full column is disabled. It is switched off rather than left to be tapped and ignored, and pressing it does nothing at all — not even a sound. The whole board is in front of you, so there is no mistake here worth scolding.
• The fall is a slide as long as the drop is tall. There is no bounce on landing, no particles and no screen shake.
• Reduced Motion — from the app’s settings or from the system — turns the fall off, and the disc is simply drawn where it landed.
• A screen reader reads a column from the bottom up, in the order the discs are stacked in it.

There is no landing preview: no shadow appears in the slot a disc would fall into while your finger is on a column. A column has exactly one landing space — the lowest free one — so a preview would tell you nothing the column does not already show, and it would cost drawing time on a slow phone for the length of every drag.

Undo, and why there is no Hint

Undo is unlimited and free, and it works from the first launch. No game feature here is ever behind an ad or a purchase, and strength is not something you unlock: all 3 opponents are available from the start.

One press takes the board back to your previous decision point, which means your drop and the CPU’s answer to it come off together. It never leaves you standing in the middle of the CPU’s turn, because that is not a position you ever decided anything from.

• It is a take-back, not a reroll. The CPU answers the position in front of it, and when two columns come out equally good it settles the tie from the match’s seed and the number of discs played — never from chance. Undo, drop into the same column, and exactly the same reply comes back.
• That determinism is held in place by a golden test, so the same match replayed after an update still answers the same way.
• There is no Hint. Nothing on this board is hidden, so a hint would have nothing to reveal — it could only name the column it would play itself, which is the CPU playing your side of the table as well as its own.
• When a match ends, the screen that comes up offers a new match against the same opponent rather than a way back into the finished position. It costs nothing and starts immediately.

The three opponents

Easy, Normal and Hard are the same program with the same judgement of a position. The only thing that changes is how far ahead each one reads before it commits.

• The search runs only when the turn is actually the CPU’s — right after your drop, or at the start of a match you asked it to open. Nothing is thinking in the background, and nothing is being computed while you sit and look at the board.
• Its disc lands about 450ms after the turn passes to it, plus however long that search takes. The pause is there so its turn reads as a turn rather than as an instant reaction, and the search runs at the end of the pause rather than inside it — which is why the budget it stops at matters.
• Hard is deliberately not the strongest opponent a computer can be. Connect Four is a solved game — with perfect play the side that opens wins — so a CPU that read to the end would only ever be an opponent nobody beats. There is no perfect-play opening database behind it either.
• Your record is kept separately for each opponent: games played, wins, losses and draws, with your total play time across all of them. No streak is counted and none is shown.

A match you abandon in order to start another one is not recorded as a loss. It counted as played the moment it began, and only a match that actually reached an end changes the record — statistics should not be something that threatens you.

Who drops first, and the match you left

Before a match you choose who opens, with You first or CPU first. You open by default, because the opening seat is the friendlier one — but a default is not a rule, and anyone who wants the harder side can take it.

The choice applies to the next match. It never touches a match already in progress: a match ends on the side it started on.

• The board is saved as you play, so leaving the screen or the app is safe. This is a turn-based game, and a saved position reopens exactly as you left it.
• There is one match slot. Tapping the opponent you are already playing resumes that match; tapping a different one replaces it, and the app asks first.
• If you leave while the CPU is thinking, the resumed match works out that it is still the CPU’s turn and plays it. The turn itself is never stored — it follows from the discs on the board and the side that opened.
• The undo history is not saved. A match you come back to starts from the position on the board rather than from the moves that built it.
• A save the game cannot trust — a disc floating above a gap, or a move count that disagrees with the number of discs — is discarded, and you are put back on the home screen instead of into a new match you did not ask for.

Reading the board

Two things decide most matches here: the centre column, and the square you hand your opponent every single time you drop.

• Take the centre early. Of the 69 four-in-a-row lines a 7×6 board contains, 51 run through the centre column and only 15 through an outside one. The CPU agrees with you about this — it adds points for centre discs and looks at the centre first.
• Every drop hands over the square above it. Before you commit, look at what your opponent would complete by landing on top of your disc. Filling the square underneath their winning square is the most ordinary way to lose a match you were winning.
• Two threats at once wins. A block can only cover one square, so a drop that leaves two different squares each completing a line for you ends the match. This is exactly where Normal gives way: it answers the threat in front of it and does not see the second one arriving.
• Block a three before you build your own. When the CPU has three in a line, take the square it needs. A line you were one disc away from is worth nothing if the match is already over.
• Against Hard, use Undo to read rather than to escape. Because a given position always draws the same reply, taking a move back and trying another column shows you where that line actually goes.
• If a match feels one-sided, change seats rather than opponents. CPU first against the same strength is a harder game than the same opponent with you opening, and it costs nothing to try.

Questions people ask