This post is just preceding this week's Sudoku. I hadn't made blogposts of my previous 2 Sudoku. The first one was made en route to Beijing for the WSC/WPC. I had no access to Facebook or BlogSpot there, so I wasn't able to make any posts. The second one I was not at home and managed to sneak in some time to make a quick Facebook post with the image, which all is a little bit faster than making posts on my blog.

The first puzzle is a variant on the X-Sums Sudoku, of which I have made a few. The variant is a bit more limiting as now not every row and column necessarily has a valid clue. This is caused by the fact that a number N has to appear in position N to become a valid clue. The construction took a while as I wanted to keep the symmetric layout and sometimes I wasn't able to make the layout symmetric as there was no longer a clue available. There are a few clues that aren't necessary for uniqueness in this puzzle, but they don't hinder the solving path and make it overall a little bit easier. I think people don't mind that my Sudokus are made a bit easier in general.

The second puzzle is a simple variant with differences. It has more given numbers than I would have wanted, but it wouldn't be unique otherwise. I wanted to make a puzzle which had a single instance of every possible Quad Difference clue possible. This of course forced one of the clues to be in a specific position as otherwise there's be no unique solution available. Which is why I went for this layout. I don't think this one is overly hard. There's a few key points in the solve where you have to use the right clues.

Rules for Sudoku
**N-Sums Sudoku:**
Clues outside the grid indicate the sum of the first N digits seen in that row or column from that side. The digit N is always indicated by the Nth digit seen from that side. In other words, it is always the last digit in the summed set of digits.

**Quad Max Difference Sudoku:**
In this Sudoku, numbers on grid points indicate the maximum difference between the four digits surrounding it. Each difference must appear at least once around each clue.