iDoku (The i Paper)

About iDoku (The i Paper)

iDoku comes from the puzzle pages of the i, the British newspaper now called The i Paper, and has run in print for years before it moved online. Clarity Media, the UK puzzle company behind the i's puzzle books, has published its rules and solving tips since at least 2010.

The grid looks like an ordinary 9x9 sudoku with a few cells shaded red. Those cells spell out the paper's letter i across the middle three boxes: a dot in the top centre box, and a stem with a foot running down through the centre and bottom boxes. On top of the usual rules, those nine cells form one more region, so 1 to 9 must appear once each inside the i as well. That makes 28 regions instead of the usual 27, and most grids cannot be finished without using the extra one.

On the website the day's grid is dated, with a strip of the past week's dates above it, a timer, and a share button once you finish. The page asks for a free account to play the daily puzzle; a subscription to The i Paper unlocks more than one puzzle a day and past puzzles.

It suits sudoku players who know the classic grid well and want one small twist that changes how the middle of the board is solved, without the arithmetic of killer sudoku.

How to play iDoku (The i Paper)

1. Open the day's iDoku in The i Paper's puzzles section and sign in with a free account or a subscription.
2. Pick an empty cell, then tap a digit from 1 to 9 on the pad beside the grid to place it.
3. Make sure each row, each column and each 3x3 box ends up with 1 to 9 exactly once.
4. Treat the nine red cells of the letter i as one more region: they too must hold 1 to 9 once each.
5. Fill every cell to finish; the page shows your time and lets you share the result.

Tips

• Start with the i: a digit already placed in one of its red cells is ruled out of the other eight, even where they sit in different boxes.
• The i crosses the middle column of boxes, so check the centre column and the centre boxes together with the i when a digit has few places left.
• No guessing is needed: if you are stuck, look for a digit that has only one place left in the i, a row, a column or a box.

Questions