Wednesday Frog

Wednesday Frog is a logic puzzle on a square pond. Frogs sit on some of the squares, lily pads and stones lie on others, and every frog hops three times — on Monday, on Tuesday and on Wednesday — always straight, two squares, over the square beside it. On Monday and Tuesday it lands on water, on Wednesday on a lily pad, one frog to each pad. Every stone must be hopped over exactly once, and no square is used twice. Nothing is given but the frogs, the lily pads and the stones; the paths are yours to find.

Here you tap a frog, then the square it should hop to, and the hop is stamped with its day: Mo, Tu or We. Tapping a square the chosen frog has already landed on takes back that hop and every later hop of that frog, and crosses serve as notes. The board will not make a hop against the rules, and says in one sentence which rule it breaks — never where to hop instead. When every frog has made its three hops and something is still off, it says only how many stones were not hopped over, not which. No hints, and nothing that checks you against the answer. And a board from a Wednesday ends differently from the boards of other days.

A new board every day — 6 × 6, 8 × 8, and 9 × 9 — 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.