Large print sudoku: expert

Solving tips

Start with the digit that already appears most often and look for the one cell in each box where it can go. When a cell is down to two or three possible digits, pencil them small in a corner. The swordfish and the XY-wing.

What makes these expert

Expert puzzles need an XY-wing or a swordfish. An XY-wing uses three cells that each have exactly two candidates: a pivot that could be X or Y, one partner that could be X or Z, and another that could be Y or Z, each sharing a row, column or box with the pivot. Whichever digit the pivot takes, one of the partners must be Z, so any cell that sees both partners cannot be Z.

A swordfish is an X-wing stretched across three rows and three columns: if a digit fits in only three columns across three rows, those rows supply all three columns, and the digit can be crossed off elsewhere in them. Both techniques reward careful, complete pencil marks, and none of these puzzles needs a guess.

Where to start on puzzle 1

These are the first moves the easiest-first method finds in puzzle 1, the same steps the hint button in Sprout Sudoku would give you:

1. Hidden single. The top-middle box needs a 3, and row 1, column 4 is the only place in that box where a 3 fits.
2. Hidden single. The top-left box needs a 3, and row 2, column 2 is the only place in that box where a 3 fits.
3. Hidden single. The top-right box needs a 9, and row 3, column 8 is the only place in that box where a 9 fits.

Stuck? The key step in each puzzle

Each puzzle below has one moment where the easy steps run out and the expert technique is needed. The digit count tells you roughly where it comes: if your grid has about that many digits filled and nothing else fits, this is the step to look for. It is written out in full, so read it only when you want the help.

Show the key steps

• Puzzle 1, with 54 of 81 digits filled (XY-wing): XY-wing: row 5, column 5 can only be 6 or 7. If it is 6, row 6, column 6 must be 2; if it is 7, row 5, column 7 must be 2. Either way one of those two is a 2, so a cell that shares a row, column or box with both cannot be a 2.
• Puzzle 2, with 53 of 81 digits filled (XY-wing): XY-wing: row 1, column 5 can only be 4 or 8. If it is 4, row 2, column 6 must be 9; if it is 8, row 6, column 5 must be 9. Either way one of those two is a 9, so a cell that shares a row, column or box with both cannot be a 9. This counts the digits ruled out by earlier steps.
• Puzzle 3, with 62 of 81 digits filled (XY-wing): XY-wing: row 3, column 5 can only be 1 or 6. If it is 1, row 9, column 5 must be 7; if it is 6, row 3, column 6 must be 7. Either way one of those two is a 7, so a cell that shares a row, column or box with both cannot be a 7. This counts the digits ruled out by earlier steps.
• Puzzle 4, with 53 of 81 digits filled (XY-wing): XY-wing: row 9, column 2 can only be 5 or 7. If it is 5, row 6, column 2 must be 3; if it is 7, row 9, column 6 must be 3. Either way one of those two is a 3, so a cell that shares a row, column or box with both cannot be a 3. This counts the digits ruled out by earlier steps.
• Puzzle 5, with 50 of 81 digits filled (Swordfish): Swordfish on 2: in rows 2, 5 and 8, the 2 fits only in columns 1, 3 and 9. Those three rows put their 2s in those three columns, so no other cell in columns 1, 3 and 9 can be a 2.
• Puzzle 6, with 44 of 81 digits filled (XY-wing): XY-wing: row 8, column 3 can only be 2 or 7. If it is 2, row 7, column 2 must be 6; if it is 7, row 8, column 4 must be 6. Either way one of those two is a 6, so a cell that shares a row, column or box with both cannot be a 6. This counts the digits ruled out by earlier steps.

Prefer a screen? Sprout Sudoku is the same kind of puzzle to play free in your browser, with hints and saved progress.

More printable puzzles

• Large print sudoku: easy
• Large print sudoku: medium
• Large print sudoku: hard
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