Girandola Sudoku: Rules and Solving Strategy

Girandola Sudoku adds a ninth-cell windmill unit

Girandola Sudoku keeps every classic Sudoku rule. Each row, column, and 3x3 box must contain the digits 1 through 9 exactly once. The twist is a set of nine specially marked cells arranged in a windmill or pinwheel shape across the grid. Taken together, those nine cells form one more Sudoku unit, so they must also contain 1 through 9 without repetition. That extra region reaches into several ordinary boxes, which means a placement in one distant part of the board can immediately restrict a marked cell somewhere else. Begin by identifying all nine Girandola cells before making any advanced deduction. Then scan the extra region exactly as you would scan a row or box: list which digits are already present, identify the missing digits, and check where each missing digit can legally go. Because each marked cell is also governed by its row, column, and box, the useful information flows in both directions. A digit excluded by the Girandola unit may become a hidden single in a row, while a row placement may create a hidden single inside the windmill.

Use the extra region to create singles and subsets

The most productive Girandola Sudoku deductions are often familiar techniques appearing in an unfamiliar shape. Suppose the marked cells still need 2, 5, and 8. If two of those cells can contain only 2 or 5, then 2 and 5 are reserved for that pair and every other marked cell loses those candidates. The remaining 8 may then become forced. Hidden pairs work the same way: if only two Girandola cells can contain 3 and 7, those digits are locked into the two cells even when each cell has extra candidates. Always cross-check the result against the normal units. A candidate removed from a marked cell can change a box from three possible positions to two, or from two to one. Conversely, a box-line interaction may remove the last alternative for a digit inside the extra region. Full candidate Notes are especially useful on difficult grids because the nine marked cells are visually separated. In Shapedoku, the same habit of treating a logical group as one unit transfers directly even though the standard game uses shapes rather than an added windmill region.

Rescan Girandola Sudoku after every marked placement

A common mistake in Girandola Sudoku is to solve a marked cell and then continue looking only at its row, column, and box. The extra region also changed, so it deserves an immediate rescan. This simple rhythm keeps the variant manageable: place a digit, update the three classic units, update the Girandola unit, then look for newly created singles and subsets. Pay special attention when several marked cells lie in the same band or stack, because their extra-region restrictions can combine with box restrictions to create locked candidates. Do not assume that the windmill pattern itself has geometric or numerical meaning beyond membership in the extra unit. The cells do not need to follow a sequence, add to a total, or match one another in any special order. Their only extra job is to contain the complete set 1 through 9 once. That simplicity is what makes the variant a good next step after classic Sudoku: the rule is easy to remember, but the scattered geometry teaches you to track a unit that is not a straight line or a box.

1. Identify all nine marked Girandola cells before solving.
2. Treat those cells as one extra unit containing 1 through 9 exactly once.
3. Scan the extra unit for missing digits, hidden singles, pairs, and triples.
4. Feed every Girandola elimination back into the crossing row, column, and box.
5. After each placement in a marked cell, rescan the entire windmill before moving on.
6. Keep complete Notes on harder puzzles so distant marked cells remain easy to compare.