# Common Sudoku Variants

Puzzle shown: Classic Sudoku by Cracking the Cryptic

There are 9 rows, 9 columns, and 9 $3\times 3$ regions. Each square must be filled with a digit from $1$ to $9$, and digits may not repeat in the same row/column/region.

In almost every sudoku puzzle, these rules will apply.

## Local Constraints

### Killer Cages

Puzzle shown: Killer Sudoku by Serkan Yürekli

Orthogonally connected cages are drawn. No digits in the same cage may repeat, and if a sum is indicated in the cage, the digits in the cage add up to said sum.

### Thermo

Digits must be strictly increasing from the bulb of the thermometer to the end.

### Arrows

Digits on the arrow must add to the digit in the circle. Digits may repeat if permitted by other Sudoku rules.

### Renban Lines

Renban lines must contain consecutive digits in any order.

### German Whispers

Two directly connected digits on a German whisper must differ by 5 or more.

### X/V

Two digits separated by an X must sum to 10. Two digits separated by a V must sum to 5. (These digits are orthogonally adjacent.)

### Kropki

If two orthogonal digits are separated by a white dot, they must be consecutive. If two orthogonal digits are separated by a black dot, one must be double the other.

### Little Killers

The digits on the diagonal indicated by a Little Killer must add to the sum indicated by the Little Killer. Digits on the diagonal may repeat.

### X-Sums

The first X digits in a row or column in the direction of an X-Sum, where X is the first digit seen in that row or column, must add to the indicated sum.

### Odd/Even

Gray circles must contain odd digits, and gray squares must contain even digits.

### Between Lines

Digits on a between line must lie between the digits on the endpoints. Digits may repeat on the line.

## Global Constraints

### Anti-knight

A square must contain a digit different from every other square a knight’s move away (2 over and 1 across).

### Anti-king

A square must contain a digit different from every other square a king’s move away (sharing a vertex).