Medium Chaos Construction Sudoku
6
3
9
2
8
4
5
8
4
9
6
7
4
8
1
3
3
2
6
3
8
5
7
1
3
8
4
2
6
3
9
1
Thick borders separate different regions. Deduce the 9 regions as you solve.
How to play Chaos Construction
Standard row and column rules apply. Nine irregular regions (separated by thick borders) must also each contain 1–9. Unlike Jigsaw Sudoku, no colors distinguish the regions - You must deduce which cells form each region from the border lines and digit constraints.
About Chaos Construction
Difficulty
★★★★☆
4/5
Constraint Type
Hidden Irregular Regions
Typical Givens
24–32
Avg. Solve (Medium)
26 min
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.
Solving Techniques
| Technique | Description | 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 Time by Difficulty
Easy
12 min
Medium
26 min
Hard
50 min
Expert
80 min