Thursday 31 March 2022
Tuesday 29 March 2022
Monday 28 March 2022
Tuesday 22 March 2022
Simple Colouring
The example here is from a puzzle which I published in February 2021. I solved it as far as I could before arriving at the position below:
I used simple colouring to move forwards as you can see in the next picture:
If row 1 column 2 is 5:
Row 1 column 7 cannot be 5.
Row 3 column 9 must be 5.
Row 5 column 9 cannot be 5.
Row 5 column 2 must be 5.
However, there is already a 5 in row 1 column 2 so this is not possible.
I will leave you to follow all the scenarios resulting from the assumption that row 1 column 2 is 5. None of them work so all the candidates marked in yellow can be removed.
The other possibility is that row 3 column 3 is 5.
This is marked in blue and does not lead to any contradictions so it is the correct answer.
Tuesday 15 March 2022
Hidden Single in a Box
I published the puzzle below in 2014:
Look at the 3x3 box or mini-grid number 6 i.e. the one with the clues 3, 4 and 8.
Where does the number 1 go in this box?
It cannot go in row 4 as there is already a 1 in row 4 column 4.
It cannot go in row 6 as there is already a 1 in row 6 column 1.
It must therefore go in row 5.
It cannot go in column 8 as there is already a 1 in column 8 row 2.
It must therefore go in row 5 column 7 as there is nowhere else for it to go.
This is called a hidden single in a box and the puzzle becomes:
Sunday 13 March 2022
Sudoku no 648 (Easy)
I created the solution for this puzzle by hand using this method described by Sudoku Guru on YouTube. Then I removed numbers at random to create the puzzle below:
Sunday 6 March 2022
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