Sudoku and Doppelblock are both grid-based logic puzzles you solve by pure deduction, so solvers naturally wonder how alike they really are. The short answer: Doppelblock is moderate to Sudoku. Below we lay out what the two share, where they part ways, and whether the skills you have built on Sudoku will carry over.
- Grid: Square, edge clues
- Closeness to Sudoku: Moderate
- Also called: Twin Block
What is Doppelblock?
Place two black cells and the numbers 1 upward in each row and column, so the clue equals the sum of the numbers trapped between the two black cells. Here are the rules in full:
- Each row and column holds two black cells plus the numbers from 1 to (n−2), each once.
- The clue outside a row or column is the sum of the numbers between its two black cells.
- The black cells hide the rest of the line from the clue.
See a Doppelblock row
Doppelblock puts two black cells and the numbers 1 upward in each row and column; the clue gives the sum of the numbers trapped between the two black cells. Here a clue of 3 sits beside a row where the numbers between the black cells (1 and 2) add to 3.
A Doppelblock board: two black cells and the numbers 1–3 fill each row and column; the outside clue sums the numbers trapped between the black cells (row 1: 1+2+3 = 6).
The "each number once per line" rule is Sudoku's own, and the sum-between-markers idea is exactly how Sandwich Sudoku works. Reaching a total from a set of digits is the same combination reasoning as a Killer cage.
What Doppelblock shares with Sudoku
- The "each number once per row and column" rule is Sudoku's own.
- The sum-between-markers idea is exactly how Sandwich Sudoku works.
- It is solved by combination logic and elimination, no guessing.
How Doppelblock differs from Sudoku
- Two black cells per line and no boxes set it apart from Sudoku.
- Only the digits between the blocks are summed, so their position matters as much as their value.
Do Sudoku skills transfer?
The "which numbers add to this total?" reasoning is the same combination skill Killer and Sandwich reward — Doppelblock just wraps it around two moving markers.
Brush up on the technique that carries over: Killer Combinations.
The verdict
Doppelblock marries Sudoku's no-repeat lines with Sandwich-style sums trapped between two blocks.
Prefer to stay with Sudoku?
If Doppelblock appeals, these Sudoku variants scratch the same itch and you can read up on each here: