How to Play Train Tracks

The rules

1. Lay one continuous track that enters the grid at A (on the left edge) and leaves at B (on the bottom edge).
2. The number beside each row, and below each column, is how many squares in that line the track passes through.
3. Each square is either empty or holds one piece: a straight or a quarter-turn curve. The track never branches, crosses itself or closes into a loop.
4. Pieces already drawn when you start are part of the answer.

The six pieces

Every track square holds one of these. Straights connect opposite sides; curves connect two neighbouring sides.

A finished example

In this small 4×4 example the track enters at A, turns down, runs along the bottom and leaves at B. Check the numbers: the top row has 0 track squares, the second row 2, the third 1 and the bottom row 2; the columns read 1, 3, 1 and 0.

Playing on this site

• Draw track: press on a square and drag into the next one. Keep dragging to lay a longer run.
• Erase: drag back over track you have drawn.
• Mark a square empty: tap it once to place an X, tap again to clear it.
• Keyboard: arrow keys move, Shift + arrow draws or erases, X marks a square, Ctrl/⌘ + Z undoes.
• Numbers turn green when a line has exactly the right amount of track, and red when it has too much.

A worked example, step by step

Here is a real 6×6 puzzle from our generator. Try it in your head before reading on.

Step 1: count

Start with the lines whose numbers leave no choice. A 0 empties its whole line, so every square in it gets an X. A line whose number equals the count of squares still available must use all of them. Each time you fill or empty a square, the lines that cross it change too, so go round again. Then use the pieces: every track square needs exactly two connections, so a track square with only two open sides must use both, and an X next to a track square closes that side.

In the picture on the right, orange lines are connections these rules force, orange dots are squares that must hold track although their direction is still open, and orange Xs are squares proven empty. That is 16 track squares and 12 empty squares before any clever thinking.

Step 2: follow the ends, avoid loops

Now look at the loose ends of the pieces you have. Each must continue somewhere, and often only one neighbour is still possible. Two rules finish the job on easy puzzles: never join the two ends of the same fragment (that would make a loop), and never join A’s fragment to B’s fragment while some row or column still needs more track (that would finish the route too early).

What to learn next

Those two steps solve every easy puzzle on this site. A few medium grids also need a parity argument, and most hard grids need a short “what if” test; both are explained with diagrams on the Train Tracks strategy page. When you are ready, try today’s daily puzzle.