Solution to Sudoku no 650

Sudoku no 650 (Extreme)

I created this sudoku puzzle by trial and error on Sudoku Solver:

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Solution to Sudoku no 649

Sudoku no 649 (Tough)

I created this sudoku puzzle by trial and error on Sudoku Solver:

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Solution to 16x16 Sudoku no 1

16x16 Sudoku no 1

I created this by trial and error at Sudoku 16 Solver:

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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.

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:

Solution to Sudoku no 648

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:

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Solution to Sudoku no 647

Sudoku no 647 (Extreme)

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Solution to Sudoku no 646

Sudoku no 646 (Tough)

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