Easter Egg
Select number by clicking a key below the Sudoku.
Apply the number into one or more boxes in the Sudoku.
If a number is wrong, select the empty key box on bottom right and then click in the Sudoku to erase the existing number.
Method
- All completed boxes are masked.
- Sets of 9x9 boxes with the search number in them are masked.
- Horizontal rows with the search number in them are masked.
- Vertical columns with the search number in them are masked.
- If a set of 9x9 boxes only has possible boxes in a single row, that row is masked in the other two sets of 9x9 boxes.
- If a set of 9x9 boxes only has possible boxes in a single column, that column is masked in the other two sets of 9x9 boxes.
- If the two 9x9 sets on the same set row do not have any possible boxes on the same box row as the third set, mask all of the third set except the boxes in that box row.
- If the two 9x9 sets in the same set column do not have any possible boxes in the same box column as the third set, mask all of the third set except the boxes in that box column.
If a 9x9 set contains only one unmasked box, it is filled with the search number.
For each possible box, the numbers in -
- the row through the box,
- the column through the box and
- the 9x9 set
are all checked to find if just one of the nine numbers is not included, in which case that number goes in that cell.
Numbers are tested continuously until all boxes are filled or no further numbers can be solved.