Summary
Basic Elimination consists of two rules. Rule 1 (Elimination): when a cat is placed, mark all 8 surrounding cells, the entire row, the entire column, and every other cell in the same color region as X, removing them from consideration. Rule 2 (Confirmation): when exactly one empty cell remains in any region, row, or column, that cell must hold a cat — place it there. A solver collects Rule 2 confirmations first and applies them before propagating Rule 1 eliminations, so that an elimination result never overwrites an already-confirmed cell and causes a contradiction.
When to use
- Apply Basic Elimination first, at the very start of every puzzle.
- Each time a cat is placed — by any technique — immediately propagate eliminations from that cell.
- When any region, row, or column has been reduced to two or fewer empty cells, a confirmation may trigger automatically.
- After any other technique (Row/Column Lock, Naked Pair, X-Wing, etc.) adds new X marks, run Basic Elimination again to check for newly available confirmations.
- When neither a confirmation nor a new elimination can be made, move on to a more advanced technique.
Why it works
The three core rules of Nyangjari — exactly one cat per row, one per column, and one per color region, with no two cats touching (including diagonals) — mean that placing a single cat immediately eliminates every other cell in its row, column, region, and all 8 neighbors. That is Rule 1. Once a group (region, row, or column) has only one empty cell left after elimination, the puzzle rules require a cat to go there. That is Rule 2. The two rules feed each other: a Rule 2 confirmation places a new cat, Rule 1 produces new X marks from that cat, and those X marks may trigger another Rule 2 confirmation. Repeating this chain until it stalls is the entirety of Basic Elimination.
Example
▲ Immediately after the cat (🐱) is confirmed at (1,1). The 8 surrounding cells, the entire row 1, the entire column 1, and all of region a are marked ×.
- Initial state: A 5×5 board with no cats placed and all cells empty.
- First confirmation (Rule 2): Counting the empty cells in region a, after row 1 is already eliminated only (1,1) remains. Rule 2 fires and a cat is placed there.
- Elimination propagation (Rule 1): Placing the cat at (1,1) marks the 8 surrounding neighbors, all of row 1, all of column 1, and all remaining cells of region a with ×.
- Chain check: Because new × marks were added, scan every region, row, and column again to see whether any group has been reduced to exactly one empty cell. If so, Rule 2 fires again.
- Termination: When no further confirmation or elimination is possible, move on to the next technique.
Watch out for
- Confirmation before elimination: Always collect Rule 2 confirmations first and apply them before running Rule 1 eliminations. This prevents an elimination from overwriting an already-confirmed cell and creating a contradiction.
- 8 neighbors vs. row/column/region: Rule 1 eliminates all 8 touching neighbors AND the entire row, column, and region. A common mistake is marking only the adjacent cells and forgetting the full row, column, and region sweep.
- Technique limit: Puzzles that cannot be solved by Basic Elimination alone require Row/Column Lock or a more advanced technique. If every remaining group still has two or more empty cells and no progress can be made, move to the next technique.
- Distinguishing from Row/Column Lock: Row/Column Lock applies when all candidate cells inside a region happen to lie on the same row or column, allowing that row or column to be eliminated in all other regions. Unlike Basic Elimination, Row/Column Lock does not directly place a cat — it only adds new X marks.