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Preparing interactive calculation engine
Preparing interactive calculation engine
Play classic 9×9 Sudoku across 4 difficulty tiers from Easy to Grandmaster. Features smart pencil candidate notes, instant custom puzzle solving, and an intelligent AI Logic Explainer that teaches you step-by-step.
When a cell has only one possible candidate remaining because numbers 1 through 9 are already distributed across its row, column, and 3×3 box.
When a number has multiple empty cells available in a grid, but can only legally be placed into one specific cell within a given row, column, or 3×3 block.
When two cells in the same unit share the exact same two candidates (e.g. [3, 7]), no other cell in that row, column, or box can contain those numbers.
An advanced strategy where a candidate appears exactly twice in two parallel rows and shares the same two columns, allowing you to eliminate that candidate from the rest of both columns.
Yes! Every generated board is verified with our backtracking validation engine to guarantee exactly one unique mathematical solution.
Yes! Switch to "Custom Solver" mode, enter your numbers, and our AI engine will solve it with full step-by-step logic proofs.
A Naked Single is a cell where only 1 number can legally fit. A Hidden Single is a number that can only fit in 1 specific cell within a given row, column, or 3×3 box.