Sudoku Learning Hub
Master every sudoku solving technique, from beginner to expert.
Full House
When a row, column, or box has only one empty cell, the missing digit goes there.
Naked Single
When a cell has only one remaining candidate after all eliminations, that candidate is the solution.
Hidden Single
When a candidate appears in only one cell within a house, it must go there -- even if the cell has other candidates.
Naked Pair
Two cells in a house sharing the same two candidates lock those digits, eliminating them from other cells in the house.
Hidden Pair
Two candidates confined to the same two cells in a house lock those digits. All other candidates can be removed from those cells.
Naked Triple
Three cells in a house whose combined candidates contain at most three digits. Those digits can be eliminated from all other cells in the house.
Hidden Triple
Three candidates confined to exactly three cells within a house. All other candidates can be removed from those cells.
Pointing Pair
When a candidate in a box is restricted to a single row or column, it can be eliminated from that row or column outside the box.
Claiming Pair
When a candidate in a row or column is restricted to a single box, it can be eliminated from that box outside the row or column.
Naked Quad
Four cells in a house whose combined candidates contain at most four digits. Those digits can be eliminated from all other cells in the house.
Hidden Quad
Four candidates confined to exactly four cells within a house. All other candidates can be removed from those cells.
X-Wing
When a candidate appears in exactly two cells in each of two rows, and those cells share the same two columns, the candidate can be eliminated from those columns.
Swordfish
The Swordfish extends the X-Wing from two rows and two columns to three rows and three columns, allowing eliminations when a digit's candidates align across three rows.
XY-Wing
An XY-Wing uses three bivalue cells -- a hinge and two wings -- to eliminate a candidate from cells that see both wings.
Skyscraper
A Skyscraper uses two conjugate pairs on the same digit that share one end in the same column (or row), forming a shape like two buildings of different heights. Candidates can be eliminated from cells that see both non-shared ends.
XYZ-Wing
An XYZ-Wing extends the XY-Wing concept with a trivalue hinge cell (A,B,C) and two bivalue wings -- one with (A,C) and one with (B,C). The common digit C can be eliminated from cells that see all three.
Unique Rectangle
A Unique Rectangle (Type 1) exploits the fact that a valid sudoku puzzle has exactly one solution. If four cells forming a rectangle across two boxes would create an ambiguous pair, extra candidates in the fourth corner must be the solution.
Jellyfish
A Jellyfish extends the fish pattern family to four rows and four columns. When a candidate digit is restricted to at most four columns across four rows, it can be eliminated from those columns in all other rows.
W-Wing
A W-Wing connects two bivalue cells with the same candidate pair through a strong link on one digit. This guarantees at least one of the cells contains the other digit, enabling eliminations.