PuzzleDayAdvanced techniques
X-Wing
Take one digit. If in two different rows it can only go in the same two columns, those four cells form a rectangle: the digit must occupy two opposite corners. That means it can be removed from every other cell in those two columns. The same logic works with rows and columns swapped.
Triples
The pair technique extends to three cells: if three cells in a unit only contain candidates from the same three digits (for example 2, 5 and 8 in any combination), those digits can be removed from the rest of the unit.
Box–line reduction
If within a row a digit can only go in cells that are all in one box, then it must be in that row inside that box, so it can be removed from the other cells of the box.
Working method for expert grids
- Place every digit you can find by scanning before writing any notes.
- Fill in complete notes for the whole grid — expert puzzles are much easier with full candidates.
- Look for pairs and pointing first, then X-Wings.
- After each new digit, rescan its row, column and box: one placement often unlocks several more.
Other challenges
Back down to hard sudoku, or test a different skill with the 7 letter word game or expert minesweeper.
Frequently asked questions
How many clues does an expert sudoku have?
About 24. The fewest clues any valid sudoku can have is 17, but grids that sparse are extremely rare; 24 is a demanding but fair challenge.
Do expert puzzles need guessing?
No. Every puzzle has exactly one solution that can be reached by logic. Some expert grids may call for advanced patterns such as X-Wing, but trial and error is never required.
Are best times saved?
Yes, separately for each level, as long as you finish without using hints.
Can I pause?
Yes. Tap the clock or press P. The board is hidden while paused so the timer stays fair, and it pauses automatically when you leave the tab.