# Flashback #20 – Product Sudoku

This puzzle was used in a final sprint round so the medium-level was appropriate. I’ll let you in on a secret; when sudoku authors run out of theme ideas, they take a blank grid, plonk in 1-9 along the main diagonal, take a step back, seek more inspiration and hope something good comes out of it.

That was pretty much how this puzzle came about.

Product Sudoku: Classic sudoku rules apply. Given numbers between two cells  indicate the product of the two numbers in those cells.

# Flashback #19 – Retrograde Battleships

So far I’ve seen retrograde tetrominoes, pentominoes, scrabble, and battleships. Retrograde puzzles are harder for writers than it is for solvers. Firstly, the author has to prove that the solution his unique (very hard to do) and, should the puzzle be too difficult for logical reasoning, solvers can always hack the puzzle by guessing (not hard to do).

Retrograde Battleships appeared in the 2000 WPC and 2001 USPC. The one that I first saw was by Cihan Altay (where is he nowadays?), and Akil Oyunlari had a puzzle book with lots of them in a Battleship variants section. I recall tediously testing all possible combinations to ensure that the puzzle had only one solution.
Thankfully, it did.
Here it is.

Retrograde Battleships: Locate the given fleet in the grid, with regard to the shapes of the cells. The ships cannot touch each other, not even diagonally. The ships may be rotated.

# Flashback #18 – Five Pair Sudoku

Let’s move on to a sudoku.
The first Five-pair Sudoku I saw was written by Vladimir Portugalov. Several followed in his Forsmarts website and his 24HPC sets. I like solving medium-ish puzzles so I keep that difficulty in mind when I’m constructing. Unless I’m out to get you (like a heavy-pointer in a puzzle set or a giant puzzle for last year’s WPC) I’m generally nice to solvers. 🙂

Five-Pair Sudoku: Classic sudoku rules apply. Additionally, each 10-cell grey area should contain two identical sets of 5 digits. The two grey areas may contain different sets.

# Flashback #17 – Tetromino Minesweepers

Back in 2012, the UKPA held its first offline event in Manchester. I believe it was the only year that the organizers posted the puzzles online simultaneously for solvers around the world to compare their scores. The reception online was dismal so that idea was abandoned later on. I contributed some puzzles and sudokus for this event and I’ll be sharing my favourites over the next few weeks.

We’ll start with a tame Tetromino Minesweepers. I first saw this variant in Thomas Snyder’s old blog but I think there might have been earlier ones elsewhere. I’d love to know the history if anyone out there knows.

Tetromino Minesweepers: Place the 7 tetromino shapes into the grid; the shapes may be rotated but cannot be reflected. The numbers in the grid indicate how many of the adjacent cells (including diagonally adjacent cells) contain pieces of the tetrominoes. The tetrominoes cannot sit on the given numbers, and cannot touch even other, not even diagonally.

# Flashback #16 – Akasuke

The last puzzle in this series of Flashbacks is the hardest of the lot. Only 1 solver (Thomas Snyder) managed to solve it. Nowadays I use a computer when writing a difficult puzzle with many deduction-paths, but back then it was all grid paper and a lot of erasing. Because of the very-restricting nature of the type, I don’t think Akasuke will see any of its siblings soon.

So here is the devil that hardly anyone solved. Have another go at this in an untimed environment.

Akasuke: Fill in the grid of shaded cells with the listed numbers. Afterwards, the numbers become Akari clues, which are used to solve Akari in the usual manner.

# Flashback #15 – Searchdoku

Searchdoku is credited to Dave Tuller in his AARP Wordsearches book. The back story of this puzzle was shared in the LMI forum. The original puzzle had a Maori-birds theme and because of the Maori language’s vowel-heavy nature, it ended up being difficult and too guess-y. This last-minute product below, finished just hours before the test was to start, was a gem.

When a puzzle is garnished with compliments, including one from logic puzzle-jesus Thomas Snyder, it means a lot to any puzzle constructor. But what excited me the most was that it got me writing for Akil Oyunlari for the next 4 years. That morning is vividly etched into my mind; I woke up late in the morning to read my e-mails. One of which was from Serkan Yurekli, who invited me to write a Searchdoku for issue 72 – which also had a similar concept.

Here is the puzzle below, can you see the break-in?

Searchdoku: Find the listed word in the grid going in any straight direction. Some words may be found in, or going through, the blank 9×9 grid. After several letters are filled in, the empty 9×9 grid becomes a Sudoku puzzle using 9 different letters.

# Flashback #14 – LITS2

LITS^2 is possibly my only creation that has caught on. There aren’t many LITS variations, let alone five years ago. The idea of cramming two pieces in each region proved to be a success as several other authors are now writing their own LITS^2.

The puzzle in the online test had a simple LMI theme. I recall tweaking for hours to get rid of that notch on the “M” – but gave up when the deadline was approaching.

LITS^2: Shade in two tetromino pieces in each bolded region. The two pieces in the same bolded region may not be adjacent to each other. Otherwise, standard LITS rules apply.

# Flashback #13 – Kropkuro

A big milestone for me has to be Puzzle Fusion, which was held during the early days of LMI back in the end of 2011. I still remember the frustration of tossing piles and piles of scrambled-up grid paper until every corner of my room was slowly drowning in litter. I completely underestimated how hard it would be to write this 24-puzzle test.

The concept was two puzzle types combining to get a hybrid type. There were 8 sets of combinations and most of the solvers’ ratings were for the hybrids. The first hybrid was Kropkuro. Please correct me if I’m wrong, but I believe this was Kropkuro’s first appearance –before it started popping up in several European tests and most recently in Matus Deminger’s Kakuro contest.

I was still new to constructing and Puzzle Fusion ended up with a really poor balance of difficulty-spread among the puzzles. The Kropkuro ended up being too massive for such a test but as a stand-alone, I’m sure it is still enjoyable to solve.
Go get it!

Kropkuro – Fill in the grid with numbers 1-9 so that each number adds up to the given sum for that row or column. No number may repeat within a single entry. A white dot is given when the two neighbouring cells contain consecutive digits. A black dot separates two numbers where one is twice the other. 1 and 2 may be separated by any coloured dot. All dots are given.

LMI, November 2011

# New Flashback Tab

Flashback (the first tag on this blog) denotes puzzles that have previously appeared elsewhere. Once every blue moon, I would stroll down memory lane of past contributions to see if any ideas can be revamped for future projects. Flashback is where I will pick a few of my personal favourites and possibly add a few words about how it came to fruition.

Links to previous Flashbacks are now on the menu above. I will occasionally add more every now and then, especially in between competitions, when the site gets a little too quiet.

# Flashback #12 – Shape Sudoku

My last puzzle for this set of flashbacks is Shape Sudoku. Shape Sudoku is near the top of my list of favourite Sudoku variants. I discovered this type in Mutant Sudoku by Wei-Hwa Huang and Thomas Snyder. The world needs more books like this! The pieces fit to spell out “24 HPC” on the grid. I’ve seen this particular puzzle in several instruction booklets long after 2011, sometimes unaccredited.

Shape Sudoku – Decide how each piece fit into the sudoku grid. Pieces can be rotated but not reflected. Then solve the sudoku in the usual manner.

Budapest, November 2011