Frog Slalom

Frog Slalom is a logic puzzle on a square pond. A frog sits on one square, a lily pad with a flower lies on another, and stones are scattered between them. The frog leaps straight along a row or a column, turns left or right after every landing, and in every leap flies over exactly one stone — a leap can be any length. The frog flies over each stone once, the route never crosses itself or comes back, and the last leap ends it on the lily pad with the flower. Nothing is given but the frog, the stones and the flower; the route is yours to find.

Here you draw the route from the frog: tap the square it should land on, and the leap joins the route. Tapping a square the frog has already landed on takes back that leap and every later one, and crosses serve as notes. The board will not make a leap against the rules, and says in one sentence which rule it breaks — never where to leap instead. When the frog gets stuck, the board says only how many stones it has yet to fly over, not where the route went astray. No hints, and nothing that checks you against the answer.

A new board every day — 6 × 6, 7 × 7, and 8 × 8 — the same for everybody, each with a single solution that reasoning alone reaches. No timer and no account needed: a board left half-done waits for you until the day turns, at midnight UTC.