Hard Train Tracks Puzzles

10×10 grids with only a handful of clues

Hard puzzles give you a 10×10 grid and usually only a few pieces beyond A and B. The route is long, and the early moves come almost entirely from the numbers, so the opening is where you win or lose a hard grid.

Our grader allows the full set of techniques here, including a one-step “what if”: suppose a square is empty (or a connection is used), follow the forced consequences, and if they break a rule, the opposite must be true. A careful solver never needs to guess beyond that single step.

Working a hard grid

Scan every row and column for the extremes first: 0s, 1s, full lines and lines one short of full. A 1 is especially useful: unless A or B sits in that line, its single track square must be a straight piece crossing the line, because any turn would need a second square in the same line.

Use parity on every cut. Between each pair of neighbouring rows, the track crosses an odd number of times if A and B lie on opposite sides and an even number of times otherwise. Combined with the row totals, that often shows a band must be crossed, or cannot be entered at all, long before individual squares are fixed.

If you are stuck, choose the square with the fewest possibilities and ask what would happen if it were empty. The contradiction usually appears within a few moves.

Hard puzzles in the daily rotation

Every Saturday and Sunday the daily puzzle is a hard 10×10 grid. Solve both to keep your streak alive through the weekend, then try the expert 12×12 grids if you want more.