Help with validation case 5: GRID

Continuing the discussion from [Community Puzzle] Optimized coloring - Puzzle discussion:

I have written two solutions - one with a greedy approach and one with a backtracking approach - that solve all the test cases correctly; and all the validation cases correctly with the exception of the validation case “05 GRID”. However, the validation case does not provide any output, so I am not sure what’s my error for the validation case.

Could anyone help me?

Other than that: loved the puzzle. Thank you @flopy78 and @David_Augusto_Villa

4 posts were merged into an existing topic: [Community Puzzle] Optimized coloring - Puzzle discussion