The Technique Academy
Sudoku techniques
The Technique Academy teaches 25 sudoku solving techniques, easiest first.
Every technique the Professor can spot, easiest first. Read the lesson, study the worked example, then try it on puzzles that need exactly this.
Easiest first
Which sudoku techniques can you learn?
Each lesson has a worked example drawn from a real board.
- Easy01
Naked Single
A naked single is a cell with only one digit left that it could possibly hold.
- Easy02
Hidden Single
A hidden single is a digit that has only one cell left to live in within a row, column or box.
- Medium03
Naked Pair
A naked pair is two cells in one unit that share the same two candidates and nothing else.
- Medium04
Hidden Pair
A hidden pair is two digits that, within one unit, can only go in the same two cells.
- Medium05
Pointing
Pointing happens when a digit's remaining places in a box all lie along a single row or column.
- Medium06
Claiming
Claiming is the mirror image of pointing: a digit's places in a row or column all sit inside one box.
- Hard07
Naked Triple
A naked triple is three cells in one unit whose candidates together draw from just three digits.
- Hard08
X-Wing
An X-Wing is a digit that appears in exactly two cells in each of two rows, with those cells sharing the same two columns.
- Hard09
Swordfish
A Swordfish is an X-Wing with a third arm: a digit confined to two or three cells in each of three rows, all within the same three columns.
- Expert10
XY-Wing
An XY-Wing is three cells with two candidates each: a pivot holding X and Y, and two pincers, one holding X and Z and the other Y and Z, each seeing the pivot.
- Hard11
Hidden Triple
A hidden triple is three digits that, within one unit, can only go in the same three cells.
- Expert12
Naked Quad
A naked quad is four cells in one unit whose candidates come from only four digits between them.
- Expert13
Hidden Quad
A hidden quad is four digits that, within one unit, can only go in the same four cells.
- Expert14
Skyscraper
A Skyscraper is a digit with exactly two possible cells in each of two rows, where one cell from each row shares a column.
- Expert15
2-String Kite
A 2-String Kite links a row and a column that each hold a digit in only two cells.
- Expert16
Empty Rectangle
An Empty Rectangle is a box where one digit's candidates lie only along a single row and a single column of that box, leaving an empty rectangle in the rest.
- Expert17
XYZ-Wing
An XYZ-Wing is a pivot cell holding three candidates, X, Y and Z, plus two pincers: one holding X and Z, the other Y and Z, each seeing the pivot.
- Expert18
W-Wing
A W-Wing is two cells that do not see each other but hold the same two candidates, X and Y, joined by a strong link on X: a unit where X has only two places, one seeing each cell.
- Expert19
Finned X-Wing
A finned X-Wing is an X-Wing with a spare candidate, the fin, tucked beside one corner in the same box.
- Expert20
Jellyfish
A Jellyfish is the fish family at its largest: a digit confined to the same four columns across four rows, with only two to four places in each row.
- Extreme21
BUG+1
BUG+1 arises when every unsolved cell has exactly two candidates except one cell that has three.
- Extreme22
Unique Rectangle
A Unique Rectangle is four cells in two rows, two columns and two boxes that could all hold the same pair of digits, which would let you swap them and get a second solution.
- Extreme23
Simple Coloring
Simple Coloring follows one digit through a chain of cells linked in pairs, each pair being the only two places for that digit in some unit, and paints alternate cells in two colours.
- Extreme24
XY-Chain
An XY-Chain is a run of two-candidate cells in which each neighbour shares a digit with the next, the chain starting and ending on the same digit.
- Extreme25
X-Chain
An X-Chain follows one digit along a chain of cells linked alternately by strong links, units where the digit has only two places, and weak links, where it merely cannot be in both.