Neighbourship Sudoku - Rules & Guide

Tip 1: Pay attention to physical limitations on edges and corners

The number of "neighbors" of a graphic grid located at the edge or corner of the disk is inherently limited! For example, a circular grid in a corner has only 3 neighbors around it, so the number filled in it can never be greater than 3 (only 1, 2 or 3 can be filled in). If it is a square grid close to the edge and it has only 2 diagonal neighbors, then the number inside can only be 1 or 2! Exploiting physical boundaries can greatly narrow down the number of candidates.

Tip 2: Find the "full" state (extreme value reasoning)

If you see a square in the middle of the board that says 4, that means its 4 diagonal neighbors must all be different numbers. What is more lethal is the edge lattice. For example, the circular lattice on the right edge in the example picture gives hint 5, and it happens to have only 5 neighbors on the edge, which means that all 5 of its neighbors must be different from each other! This full status creates strong exclusivity.

Tip 3: Use the numbers in the shape itself

Don’t forget that the square and circular grids themselves are part of Sudoku. If in reasoning you find that the four diagonal neighbors of a square have only 2 different numbers, then the square itself must be filled with 2. On the other hand, if when deriving other rules it is discovered that the square grid cannot be filled with 2, then it is absolutely impossible for its diagonal neighbor to have only 2 different numbers. This forms a reverse logical lock.

Example image: special grid containing circular and square statistical conditions

A: Assume that the four diagonal neighbors of a square grid are eventually filled with numbers 1, 3, 1, and 4 respectively. There are a total of 3 different numbers 1, 3 and 4. Therefore, the number 3 must be filled in this square grid.

A: Yes! This is also the greatest fun of Neighborhood Sudoku. Whether it is a graphical grid with pre-given hint numbers or an empty graphical grid, as long as it has an outer frame, the number you finally fill in the grid must perfectly fit the statistical results of non-repeating numbers in its surrounding neighbors.