Corner Rules: Mastering Nurikabe’s Extra Restrictions

Nurikabe is a numbered-grid map of islands separated by an unbroken black sea. This guide explains how to solve a Nurikabe puzzle with diagonal constraints by adding a corner test to the familiar island-and-sea method. White cells belong to numbered islands, while black cells must connect without forming a solid 2×2 block. Learn more about Sravneniye Populyarnykh Programm Dlya Zapisi Qso Hrd Logger32 N1mm Basics.

The word diagonal is not standardised. Some sets forbid black cells from sharing a corner; others prevent separate islands from touching diagonally or provide drawn links. The logic below assumes two black cells may not touch at a corner. A supplied legend always takes priority. Learn more about Competitions.

Australian solvers often take a puzzle to a café in Melbourne or work on one during a train ride between Sydney suburbs, keeping island shapes in a small notebook. A puzzle book from Dymocks or a free online sheet needs little equipment beyond a pencil and fine eraser. Short lunch-break attempts suit a workday, while a quiet evening can accommodate a longer grid.

Read the Rule Before the Clues

Begin by separating the base Nurikabe conditions from the added restriction. Every numbered cell starts white and identifies an island whose size equals the clue. Islands cannot touch along an edge, all black cells must form one connected sea, and no 2×2 area can be entirely black.

Then identify exactly what the diagonal rule prohibits. Under the version used here, edge contact between black cells is legal, but corner contact is not. Ordinary Nurikabe permits some diagonal black contacts, so do not import that assumption. If a set bans diagonal contact between islands, check white pairs too; explicit links should be settled before colouring the sea.

Give every square one of three working states: confirmed white, confirmed black, or undecided. Note tentative choices when an island has several possible shapes. This notation makes later colour changes visible and prevents a guess hardening into false certainty.

Grow Islands From the Numbers

Place each clue in the white group and treat its orthogonal neighbours as possible island cells, not automatic walls. A square touching two clues cannot be white, since it would merge islands, while one touching a single clue may extend that island. Work outward while respecting the exact count.

A 1 clue fixes its island as one white square, with every edge-neighbour black. Larger clues need a connected shape of the required size, which need not be square or symmetrical. Finish the smallest islands first, as their black borders create firm placements for the rest of the grid.

The diagonal rule affects growth when a proposed black border would touch an existing black cell at a corner. Before colouring it, check whether the square should instead belong to the nearby island. For example, a 3 clue might need a bent path around another island rather than the compact L shape that first appears.

Use Corner Logic to Resolve Conflicts

A 2×2 check becomes stronger when both restrictions are combined. A legal block may contain no black cells, one black cell, or two black cells sharing an edge. Opposite black corners are illegal because they touch diagonally; three or four black cells are also illegal.

When opposite corners are black, one must eventually become white, or one was misclassified earlier. Do not change a numbered clue merely to break the conflict. Inspect the surrounding island to see which cell can legally join it, then follow the resulting black placement to check whether it removes the touch.

Conflicts often form chains. A checkerboard-like patch may contain several corner touches, and correcting one can expose another. Mark uncertain cells lightly, resolve the pair supported by the strongest island evidence, and rescan affected 2×2 areas. This local loop is faster than completing the sea before noticing incompatible corners.

Keep the Sea in One Piece

Black cells connect only through shared edges; diagonal proximity never joins sea sections. After placing black cells, trace each isolated pocket to the main wall and identify the missing connection. A pocket beside a numbered island often results from colouring too much black early, so loosening a tentative wall can repair both connectivity and shape.

Avoid painting long black bands across open areas before the islands are secure. Such bands can seal off a future route or trap a clue cell. Use confirmed borders as anchors, extend the sea in short steps, and check after each step that no new corner pair appears.

Digital checking can help with routine audits, although generic solvers may not recognise a custom diagonal rule. This [QSO logging comparison] for ham-radio operators shows that filters, alerts, and platform support matter more than a polished display. A Nurikabe checker likewise should expose each violated condition clearly, while manual corner verification remains essential.

Finish With a Full Audit

Check the finished grid in a fixed order. Count every island and confirm that it contains only its own clue. Look for edge contact between islands. Inspect every 2×2 block and diagonal black pair. Finally, trace the entire black sea and confirm that no section has been stranded.

Timing works best when deductions are separated into passes. In a twenty-minute lunch break, establish obvious island sizes and eliminate diagonal conflicts before tackling sea connectivity. Longer Australian evenings can focus on remaining chains, while a photograph of the grid helps compare tentative marks after a break.

Competition calendars make practice more focused. Zagonetka.net’s [Croatian tournament schedule] is a useful place to watch announcements, results, and details of Croatian and international events. Croatia is usually eight or nine hours behind Melbourne and Sydney, so Australian evenings can overlap European afternoons, though daylight-saving changes alter exact times. Checking islands first, corners second, and connectivity last exposes any decisive error before time expires.