This is a Melon puzzle. (24 – Digital Snail)
or solve online (using our beta test of Penpa-Edit tools; use tab to shift between number entry and shading modes.)
Theme: WPC Practice
Rules: Enter digits 1 through 4 into some cells so that each row and column contains each digit exactly once. Also, along the snail (from the upper-left corner and spiraling to the center) digits must occur in 1-2-3-4-1-2-3-4-… order. Some clues are given in the grid in the form of lit digital segments. Each of these cells must contain a digit, and that digit must have that segment lit in the form shown below the puzzle.
Or see an example from the WPC instructions using 1 to 3 here.
Answer String: Enter the marked rows from left to right, separating the two rows by a comma. Use an X (capital letter) for each empty square.
Time Standards (highlight to view): Grandmaster = 6:00, Master = 8:30, Expert = 17:00
Solution: PDF
Very difficult to make headway near the start-middle of the solve. Enjoyable nonetheless, like all of Melon’s puzzles.
Wow this was a great hard puzzle! What made me break trough was a change of Notation: instead of Numbers 1 to 4 i switched to letters a to d. That allowed me to give them index numbers from a1 to d8 which made the solving path a lot simpler for me