如何玩外部数独

Outside Sudoku is a variant where digits appear outside the grid's borders, one or more per row and per column. Each outside digit must appear somewhere within the first three cells of the row or column it points into (the nearest three to that outside clue). Standard Sudoku rules apply throughout.

Each outside clue constrains only the first three cells of its row or column — the three cells nearest to where the clue is placed. A clue on the left side of row 5 means that digit must be in column 1, 2, or 3 of row 5. A clue on the top of column 4 means that digit must be in row 1, 2, or 3 of column 4.

Yes — the clue only guarantees the digit is somewhere in those first three cells, not which one. When multiple outside clues constrain the same three-cell window, their interactions can pin specific cells very precisely. Cross-referencing horizontal and vertical outside clues is the primary solving technique.

The rule is simple but the deductions require careful accounting of which digits must appear in which windows. Easy puzzles are accessible for Sudoku players of all levels. Harder puzzles demand systematic tracking of all outside constraints simultaneously across every border.

Find rows or columns where outside clues constrain all three cells in the first window. If three different clues each point to the same window, those three cells are fully determined in terms of which digits they contain (though not necessarily in which order). This is the fastest path to early placements.

Easy puzzles take 8–18 minutes. Medium puzzles run 18–35 minutes. Hard puzzles average 35–65 minutes and expert puzzles can exceed 90 minutes. The key variable is how many outside clues are provided and how tightly they constrain each three-cell window.