The Grid with the Green Cells

So a friend wanted me to try out the reverse-puzzling riddle he created. It consisted of a 4x4 grid with a digit in each cell and a single closed loop drawn along the edges of its cells. Also some of the cells were highlighted in green.

You were supposed to answer the following questions:

  1. What does it mean for a cell to be green?

  2. Which two types of puzzles inspired this one?

But to be honest, answering those questions was way too trivial given the complete grid, so I suggested to remove the digits and the loop from the grid and see if people would still be able to answer both questions. They were not, because we forgot to mention that the loop was somehow involved.

Given that story and the image, your actual task is to recreate the initial grid by filling in the correct digits and the correct loop!

If your assumptions about the rules are correct, this solution will be unique.

Comments with questions, solutions and/or deductions are highly appreciated.


1 Answer 1


The grid is

a Sudoku with 0-3; green squares represent valid Slitherlink clues.

I couldn't find a logical path to reconstruct it; here's the solution I found through trial and error.

enter image description here

  • $\begingroup$ Couldn't the loop pass the other 2 sides of the top left cell? OP said solution is unique, so this would flout that... Or is there an erroneous ambiguity in the original puzzle, do you think? $\endgroup$
    – Stiv
    Mar 22, 2020 at 17:22
  • 1
    $\begingroup$ @Stiv Then the cell in row 1, column 2 would be green. $\endgroup$
    – Deusovi
    Mar 22, 2020 at 17:23
  • $\begingroup$ Ah, I see - so you would assume that any cells that were invalid remain unshaded... Got it. $\endgroup$
    – Stiv
    Mar 22, 2020 at 17:24
  • $\begingroup$ Yes that is the correct solution! As there are a ton of green cells in the bottom right and rot13(mrebrf ner irel erfgevpgvir) you either get the correct solution or you get inconsistencies very quickly if you start by rot13(cynpvat gur mreb va gur obggbz evtug frpgbe) $\endgroup$
    – Zilvarro
    Mar 22, 2020 at 17:30

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