Suguru (Tectonic)

Suguru, also known as Tectonic or Tectonics, is a number-placement puzzle played on a grid divided into irregularly shaped groups (regions) of cells. Each region of size N must be filled with the digits 1 through N. The key constraint is that identical numbers may not touch each other — not even diagonally. This "no touching" rule for equal digits creates a web of interacting constraints that makes Suguru deeply satisfying to solve.

Rules

1. The grid is divided into irregular regions (groups) of varying sizes, typically from 1 to 5 cells.
2. Each region of size N must contain the digits 1 through N. A region of 3 cells gets digits 1, 2, 3; a region of 5 cells gets digits 1, 2, 3, 4, 5; and so on.
3. A region of 1 cell always contains the digit 1.
4. Identical digits may not be adjacent in any direction — horizontally, vertically, or diagonally. Every cell has up to 8 neighbors, and none of them may contain the same digit.
5. Some cells are pre-filled with clue numbers.

Strategies

• Single-Cell Regions: A region of size 1 always contains 1. This immediately constrains all eight neighboring cells (none can be 1).
• Neighbor Elimination: When a digit is placed, it is eliminated as a candidate from all 8 surrounding cells. This cascading elimination is the primary solving mechanism.
• Forced Digits: If a region has only one cell where a particular digit can go (after elimination), that digit is placed there.
• Naked Singles: If a cell has only one remaining candidate after all neighbor constraints are applied, that candidate is the answer.
• Region Interaction: Two adjacent regions share a border. Digits used near the border of one region constrain what can appear in the neighboring region, even for cells that are not direct neighbors.
• Diagonal Chains: A sequence of diagonally adjacent cells can propagate constraints across the grid. If cell A contains 3, no diagonal neighbor can be 3, which may force placements further along the chain.

Suguru was created by the Japanese puzzle designer Naoki Inaba, a prolific inventor known for creating dozens of original puzzle types. Inaba first published the puzzle in the early 2010s, and it quickly attracted attention in the puzzle community for its elegant combination of simple rules and challenging deduction.

The puzzle is known by different names in different markets. In the Netherlands and Belgium, it gained wide popularity under the name "Tectonic," published by Denksport and other puzzle magazines. The name "Tectonic" evokes the idea of tectonic plates — irregular regions that fit together to cover the earth's surface, much like the puzzle's regions cover the grid. In Japan, the original name is "Number Blocks" or simply "Suguru."

Suguru/Tectonic experienced rapid growth in European puzzle markets during the mid-2010s, where it was embraced as a fresh alternative to Sudoku. Its appeal lies in several factors: the rules are simpler than Sudoku (no row/column constraints, just region filling and no-touching), the diagonal adjacency rule creates a different spatial dynamic, and the irregular region shapes give each puzzle a unique visual character.

The puzzle has appeared in puzzle competitions and is featured on online puzzle platforms. Its accessibility makes it suitable for beginners — small grids with large regions are very easy — while large grids with small regions can challenge experienced solvers. The "no diagonal touching" rule is particularly notable because it is rare among number-placement puzzles, giving Suguru a distinct identity in the crowded field of grid logic puzzles.