Chaos Construction
You must determine the region boundaries as part of solving
Easy
Chaos Construction Easy
Medium
Chaos Construction Medium
Hard
Chaos Construction Hard
Expert
Chaos Construction Expert
What is Chaos Construction?
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
| Constraint type | Hidden Irregular Regions |
| Typical givens | 24–32 |
| Difficulty rating | ★★★★☆ 4/5 |
| Avg. solve time — Easy | 12 min |
| Avg. solve time — Medium | 26 min |
| Avg. solve time — Hard | 50 min |
| Avg. solve time — Expert | 80 min |
How to Solve Chaos Construction
| Technique | What it does | Level |
|---|---|---|
| Border Reading | Thick borders separate cells in different regions. Cells without thick borders between them are in the same region. Map connected groups first. | Beginner |
| Region Size Counting | Each region contains exactly 9 cells. Count connected groups to verify region membership and identify boundaries. | Intermediate |
| Deducing Regions from Digits | If standard row/column logic places a digit, use that placement to confirm or deny region membership — a region can only contain each digit once. | Intermediate |
| Region Pointer Pairs | If a digit in a deduced region is confined to one row or column, eliminate it from that entire row or column. | Advanced |
| Construction and Solving Together | Alternate between deducing region structure and placing digits — each informs the other in a co-dependent process. | Advanced |
Average Solve Times
Easy
12 min
Medium
26 min
Hard
50 min
Expert
80 min
Frequently Asked Questions
How do I identify the regions?
Thick borders mark region boundaries. Connected groups of cells without thick borders between them form a single region.
Is Chaos Construction harder than Irregular Sudoku?
Yes — the hidden region structure adds a meta-solving layer on top of the digit placement challenge.