Swudoku

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A full sudoku grid with its numbers in the wrong cells: swap tiles until it is solved.

Play Swudoku

on swudoku.com

Swudoku #501 at the start: a full 9x9 grid with yellow tiles already home, grey tiles still to swap, and a target of 27 to 54 swaps

Swudoku is a daily sudoku played by swapping. The 9x9 board starts full, but its numbers sit in the wrong cells, and you swap pairs of tiles until every row, column and block is right. Your score is the number of swaps you used, so players come back each day to beat their count and compare it with others.

About Swudoku

Swudoku turns the sudoku grid inside out. Instead of filling empty cells, you get a board that is already full of digits, all of them present in the right numbers but scattered into the wrong places. You tap one tile, then another, and the two trade places. When every row, column and 3x3 block contains 1 to 9 once each, the puzzle is solved.

The game is made by Robert Stinson and is played on swudoku.com and in an iOS app. There is one board a day, the same for everyone, and each one is numbered. There is no timer: the score is simply how many swaps you used, and lower is better. A move that puts both tiles into their correct cells at once is a Double Swap, and the best scores for a board, which the game calls GOAT territory, are made mostly of those.

Colour does much of the work of reading the board. Grey tiles are in the wrong cell, yellow tiles are home but sit in an unfinished row, column or block, green tiles belong to one complete group and dark green tiles are fully finished. Undo takes back a swap at no cost, so a move that made things worse can be reversed.

The daily board plays without an account and without ads. A free account saves your scores, syncs them between the web and the app, shows a histogram of how other players scored on the same board, and opens the archive of past puzzles on the web. The iOS app offers only the day's puzzle.

It suits sudoku players who want something different from filling in pencil marks, and players of swap games like Waffle who would enjoy the same idea on a number grid.

How to play Swudoku

Open today's board on swudoku.com or in the iOS app; the grid is already full.
Study the board before moving: grey tiles are in the wrong cell, yellow tiles are already in place.
Tap a tile to select it; it turns blue.
Tap a second tile to swap the two, then watch how the colours change.
Keep swapping until every tile is dark green, meaning each row, column and 3x3 block holds 1 to 9 once.
Check your result screen for your swap count and Double Swaps, and share it if you like.

Screenshots

Swudoku share image: a phone showing a 9x9 swap sudoku board with grey, yellow and green tiles, beside the Swudoku name

Tips

Look for Double Swaps first: two grey tiles that each belong in the other's cell fix two cells in one move.
Start with obvious clashes, such as a row or column holding the same number twice.
Work through one row, column or block at a time instead of jumping around the grid.
Watch for cycles of three or four tiles that rotate through each other's cells, and plan the whole cycle before you start it.
Use Undo freely; it costs nothing, so a swap that turned tiles grey can be taken back.