Normal sudoku rules apply.
A number in a grey cell X, is part of a string of numbers that is X cells long. The string forms a straight line going either horizontally or vertically. Each number in the string is consecutive with any number next to it in the string.
One such horizontal string that is just a subset of a longer such horizontal string does not create a grey cell. Likewise one such vertical string that is just a subset of a longer such vertical string does not create a grey cell.
A string consisting of just one number is valid.
All possible grey cells are given.
Example:
The puzzle:
solving online: penpa
Solution code: Column 4, top to bottom, no gaps between numbers.
on 10. March 2021, 03:09 by bigger
That 1 is fun