Sudoku Companion

This program will be your companion when playing sudoku. It's also a solver willing to explain when needed.
Landscape and portrait modes are accepted, and the display is similar on all types of devices.

16599 puzzles grouped in 4 different levels of difficulty are present.
You may import your own grids:
• OCR: let the camera capture the content of a printed puzzle
• file: import a file with puzzles
• edition: use the editor to enter new puzzles by hand
• clipboard: use copy-paste functionality.

Play with or without visible candidates (pencil marks).
Get hints or explanations on applicable techniques.
Use unlimited two ways history do / redo with mark / return to mark.
Complete in some seconds the exploration of all techniques applicable for a given puzzle.
Save current session (with its history) to alternate playing several grids.

★★ The puzzles ★★
The internal puzzles are ordered by increasing difficulty.
The following techniques may be needed
• easy (9603 puzzles): unique (singleton), hidden unique
• medium (4379 puzzles): blocked (bloc - line or block - column interaction), hidden blocked, nude pairs, nude triplets
• hard (1964 puzzles): hidden pairs, hidden triplets, x-wing, swordfish, xy-wing, xyz-wing, xy-chaine
• very hard (653 puzzles): nice loop

★★ OCR ★★
To seize a printed puzzle by OCR will need some cleverness: perfect (very) close-up focus, no motion-blurring, filling up the square window with the puzzle grid but a tiny white margin. Check that all the digits are correct, and if not change them by hand - or retry OCR. Don't forget "done" to leave!

★★ Import export ★★
To import a file with puzzles, copy the file to a convenient folder on the device, then use the option "find" of the import dialogue. Next step suppose you have installed a file exploration application like Android File Manager, and select this one from the applications listed. You then navigate to the folder with the file to import. The file format should be SDM (one puzzle by line - however the file extenson is not checked).
To export, do a long tap on the grid and choose one of the "copy" options.

★★ Saving a session ★★
On program closing the current session is registered to be reloaded next time.
To save a session at any moment while playing, do a long tap on the grid and choose "save session".
When the saved sessions are displayed, a long tap on an item lets you delete the session.
Saving a session is a means to store puzzles imported by OCR, edition or pasting.