How to Play Chaos Construction
You must determine the region boundaries as part of solving
The Rules
Standard Sudoku rules apply: fill every row, column, and 3×3 box with the digits 1–9, each appearing exactly once.
Chaos Construction Sudoku gives you no pre-defined regions at all. Instead, you must deduce both the digit placements AND where the nine 9-cell regions are located, while satisfying all standard Sudoku row/column rules. This is the most open-ended Sudoku variant — the puzzle defines enough constraints (often through lines or other rules) to uniquely determine both the grid and the region structure.
At a Glance
How to Solve Chaos Construction
Common Questions
What is Chaos Construction Sudoku? ▾
Chaos Construction Sudoku (also called Uncoloured Irregular Sudoku) is a variant where the nine irregular regions are not shown at the start. Instead, only thick border segments are given — you must deduce the boundaries of the nine regions as part of solving the puzzle. Once you determine a region, it must contain 1–9 exactly once.
How do I find the hidden regions? ▾
Thick line segments between cells mark regional boundaries. By following these boundaries and counting cells, you can begin to infer where each region begins and ends. A complete region always contains exactly nine cells. Cross-referencing digit placement constraints with possible region shapes is the core meta-solving step.
Do Sudoku rules still apply? ▾
Yes. Every row, column, and the nine hidden irregular regions must each contain 1–9 exactly once. The regions are standard in size (9 cells each) and follow all the same rules as Irregular Sudoku — the only difference is that you must deduce the region boundaries as you go.
Is Chaos Construction Sudoku very hard? ▾
It is among the most challenging Sudoku variants. The region deduction layer adds significant complexity on top of standard Sudoku logic. Expert Chaos Construction puzzles are considered some of the hardest logic puzzles available. Even easy difficulty requires more concentration than most other variants.
Where do I start in Chaos Construction Sudoku? ▾
Begin at corners and edges — border segments there are most constrained. Count cells along each segment to identify which regions are smallest and most bounded. Once you confirm a single full region, the digit constraints it introduces often help you trace the adjacent region boundaries.
How long does Chaos Construction Sudoku take to solve? ▾
Easy puzzles take 20–40 minutes. Medium puzzles run 40–75 minutes. Hard and expert puzzles can take well over 2 hours. The region deduction phase alone often takes longer than solving a complete standard Sudoku.