Sudoku X — printable PDFs
Sudoku X is Classic with two extra units: the main diagonal (top-left to bottom-right) and the anti-diagonal (top-right to bottom-left) each must contain digits 1–9 exactly once. The diagonals show on every page as thin lines so you always see which cells fall on them. The extra constraint earns its keep on the 81-step solve — placements that look ambiguous from rows and columns alone often collapse when you scan the diagonal.
Rules: standard Sudoku rules plus both diagonals must contain digits 1–9 with no repeats. Scan the diagonals every time you scan rows and columns — the diagonals share digits with three different rows, three columns, and three boxes, so a single diagonal placement often unblocks four or five other cells at once.
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Easy
Easy puzzles are solvable with plain row, column, and box scanning — no pencil-mark techniques required. A good choice for kids learning the rules, for warm-ups, or for a relaxed evening solve.
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Medium
Medium puzzles start to need basic pencil-mark techniques: naked pairs (two cells in a unit that can only be two specific digits) and hidden singles across wider units. A typical solve runs 7–15 minutes.
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Hard
Hard puzzles introduce locked candidates, pointing pairs, and box-row interactions. Expect 15–25 minutes per puzzle if you're comfortable with those techniques — and steady pencil-mark discipline.
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Expert
Expert puzzles lean on X-wings, coloring, and combined chain logic. Not a starting tier — but a natural step if you've been finishing Hard in ten minutes or less.
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