Workshop › Sudoku › Step 28 of 28

Build it yourself: undo

What we are doing

Everyone makes mistakes. Keep a list of the changes you make, and let U (or Ctrl+Z) undo the last one, putting back the digit that was there before.

Your turn

• Each digit you write or erase is remembered, with the digit that was in the cell before.
• U (or Ctrl+Z) takes back the last change, selects that cell, and can be pressed again for older changes.
• A new game starts with nothing to undo.

Skills: Arrays and objects, Keyboard and mouse input

← Tap the pad

All steps

1. Nine by nine
2. Lines and boxes
3. A puzzle from a string
4. The puzzle's own digits
5. Keep drawing
6. The selected cell
7. Light up row, column and box
8. The same digit everywhere
9. Click to select
10. Move with the arrows
11. Write digits
12. The three rules in one loop
13. Show mistakes
14. Solved!
15. A clock
16. The solved message
17. Play again
18. The easiest cell
19. The solver
20. Random order
21. Invent a puzzle
22. A new puzzle every game
23. Hints
24. Best time
25. N for a new puzzle
26. A number pad
27. Tap the pad
28. Build it yourself: undo