Suguru

Each region holds the digits 1 up to its own size — and no two touching cells anywhere, diagonals included, may match.

What it is

A grid carved into irregular regions of up to five cells. A region of size k contains each digit 1..k exactly once, and identical digits never touch, not even at a corner. A handful of givens starts the chain.

How to play

Singletons and pairs place themselves. From there the touch rule does the work: a placed digit sweeps its eight neighbours clean, which often collapses a nearby region to one arrangement. Feel for the 2×2 blocks — four mutually touching cells always need four different digits, and that observation cracks most middle-game positions.

Purpose

A fast-growing newspaper genre (also sold as Tectonic) that slots straight onto the shared solver: the region rule is AllDifferent unchanged, and the touch rule is one elimination propagator. It also taught the workspace a geometry lesson worth recording: a 2×2 block is a 4-clique under the touch rule, so regions and digits cannot be generated separately — the carve has to respect what the blocks can still drink from.

History

Invented by Naoki Inaba as Nanba burokku (number blocks); published across Europe as Suguru or Tectonic, where it has become a daily-paper staple.

This implementation

• Spec knobs: size (5–9), difficulty, cell, line.
• Generation: regions of three to five cells by seeded growth with boxed-in leftovers absorbed into neighbours; a Hall’s-condition check on every 2×2 block rejects uncolourable partitions before any search; the shared solver’s own search fills the survivors; digits are then dug out one at a time while the ladder still finishes the board at the requested ceiling.
• Guarantees: deterministic per seed; exactly one solution, proven by exhaustive count; solvable by inference alone; rated by the hardest technique the solve actually used.