Medium Thermo Sudoku
6
8
5
3
2
9
6
1
6
4
9
7
1
7
4
2
7
5
6
9
2
8
1
9
7
4
5
8
3
5
1
2
How to play Thermo Sudoku
Standard Sudoku rules apply. Extra rule: digits along each grey thermometer must strictly increase from the bulb (circle end) to the tip. A 3-cell thermo could be 2,5,8 or 1,4,9 but not 3,3,7 or 5,4,8.
About Thermo Sudoku
Difficulty
★★★★☆
4/5
Constraint Type
Line Constraints
Typical Givens
20–28
Avg. Solve (Medium)
22 min
Thermo Sudoku overlays thermometer shapes on the grid. Each thermometer has a bulb (circle) at one end and a tip at the other. The digits along any thermometer must strictly increase from the bulb to the tip. Combined with standard Sudoku constraints, this creates powerful chains of deductions — knowing the bulb is at least 1 and the tip is at most 9, you can calculate the range of valid values for each cell on the thermometer based on its position.
Solving Techniques
| Technique | Description | Level |
|---|---|---|
| Range Restriction from Length | A thermometer with N cells must use N strictly increasing distinct values. The bulb is at least 1 and the tip is at most 9, giving a calculable valid range for each cell. | Beginner |
| Minimum/Maximum Bounding | The bulb value is ≤ 9 − (N − 1). The tip value is ≥ N. Apply these bounds immediately to prune all thermometer candidates. | Beginner |
| Overlapping Thermometer Deduction | Two thermometers sharing a cell give tighter combined bounds than either alone. | Intermediate |
| Forcing Chains via Thermometers | When a value is forced into a thermometer cell, all cells closer to the bulb must be smaller and all closer to the tip must be larger. | Advanced |
| Short vs. Long Thermometers | A 2-cell thermometer is simply a greater-than relationship. A 9-cell thermometer forces exactly 1–9 in order. | Intermediate |
Average Solve Time by Difficulty
Easy
10 min
Medium
22 min
Hard
45 min
Expert
75 min