Path Pairs

How to play

Drag from a letter to draw its path, with a mouse or a finger. Let go to stop; pick the path up again from its own head. With a keyboard, Tab reaches the board once and the arrow keys move around it — Enter picks a path up, and the arrow keys then draw it.

Every letter appears exactly twice. Paths run up, down, left and right, never diagonally, and no two paths may share a square.

Joining every pair is not finishing on its own. In every preset but Relaxed, every square must end up on a path — the shaded squares are the ones still to cover.

Rules and controls

• Each letter appears twice, and the two must be joined.
• Paths move one square at a time, never diagonally.
• A square belongs to one path. Paths cannot cross or overlap.
• A path cannot branch — it is one line from a letter to its twin.
• Drawing through another path cuts that path back to just before the square you took.
• Except in Relaxed, every square must end up on a path before the board is finished.
• Undo and redo go a whole stroke at a time — U and R, or the buttons.

Modes

• 5×5 — Five pairs on a small grid. The place to start.
• 7×7 — Twelve pairs, and rather more to keep track of.
• 9×9 — Twenty-two pairs and a board that fills right to the edges.
• Relaxed — The same boards, but you only have to join the pairs — empty cells are fine.
• Daily Paths — One board, the same for everybody, seeded by the UTC date.

Tips

• Start in the corners. A letter in a corner has two ways out at most, and often only one, so those paths are the ones that are already decided.
• Watch the edges. A path that runs along an edge and leaves a single square stranded behind it has gone wrong, because that square can never be covered.
• Two letters next to each other are usually not joined by the short route. If they were, the squares around them would have nothing to cover them.
• Draw freely. Cutting through another path is a normal move, not a mistake, and undo takes back a whole stroke.
• If the letters are all joined and squares are still empty, one of the paths is taking the short way round. Look for the one with the most room beside it.

Privacy and local play

Everything runs in your browser. Your current board, your settings and your best times are kept on this device only, and the button under the board clears them without touching any other Zerdly tool. No account, no sign-in, and nothing about your play leaves the machine you are on.

Questions

What happens if I draw through another pair's path?

That path is cut back to just before the square you took, and everything before it stays. The move is not refused. Reusing space is most of the work on a big board, so making you clear the other path first would be several seconds of tidying for every idea you wanted to try. Dragging back along your own path erases it the same way, one square at a time.

I have joined every pair. Why does it not say solved?

Because in every preset but Relaxed, every square has to end up on a path. A board with all its letters joined and three empty squares is not finished. The top strip shows how many squares are covered, and the uncovered ones are shaded. If you would rather only join the pairs, Relaxed removes that rule.

How is Relaxed different from the 7×7 preset?

It is the same size of board at the same difficulty. What changes is what finishing means: you only have to join the pairs, and empty squares are fine. Its best times are kept in their own table, because a time from a run that did not have to cover the board is not comparable with one that did.

Does every board have exactly one solution?

Yes, and it is proved rather than assumed. A board is built by cutting a single path that already covers every square into pieces, then a solver counts the answers; it is kept only when there is exactly one. If the search runs out of its budget the board is discarded rather than shipped with a guess.

Why do two pairs have the same colour?

Because there are eight colours and a 9×9 board has twenty-two pairs. Colour here is only there to help two paths crossing near each other read as two paths — the letter is what says which pair a square belongs to. Twenty-two colours a colour-blind player could tell apart do not exist, so nothing on this page depends on colour alone.

Does the hint ever guess?

No. It searches from the position you are actually in and names the next square of one path, so it always fits what you have already drawn. It is worked out fresh each time and can never be advice about a position you have undone. Boards finished with a hint still count as solved, but they do not set a best time.

What do the difficulty names mean?

A band is measured by solving the board rather than attached to it by the generator: it counts the work a full proof of uniqueness costs. Gentle boards fall out quickly, Steady ones need some backtracking and Tricky ones need a good deal. The cuts differ by size, because a bigger board takes more work at every level.

Can I undo a whole drag?

Yes — undo goes back one stroke, not one square. A drag across fifteen squares is one thing you did, so it comes back as one. Backspace erases the whole path under the cursor, and Clear board starts again.

How does the daily puzzle work?

One board a day, the same for everybody, built from the UTC date rather than your local one. Your result and your streak are kept on this device and nowhere else, and the board is regenerated from the date rather than stored — which is why the version is part of the key.

Is anything sent to a server?

No. The generator, the solver, the hints, the sounds and your progress all run in your browser. There is no account, and clearing this game's data leaves every other Zerdly tool untouched.

Related interactives

• Slitherlink — the other route where you draw a line and the shape of it is the answer.
• Bridges — join numbered islands into one connected network.
• Kakuro — sums across and down, with one answer.
• Arithmetic Cages — a Latin square with arithmetic clues over it.
• Codebreaker — deduction against a hidden answer.