It's January first, and the calendars around here are already mixed up!

It will take someone with a good mind for puzzles, and with a thorough knowledge of the calendar. It will take someone like...you, perhaps?

To kick off 2012, I posted a new puzzle in the Mental Gym, which I call the Sliding Calendar Puzzle! It's a blending of two feats already in the Mental Gym, the Day of the Week For Any Date tutorial and the 15 Puzzle tutorial.

When you first go to the link, it initially looks like a calendar, with a month and year above, and the days of the week just below that. Unfortunately, the days themselves are scrambled, as shown below.



Note that there are two different types of pieces. The blue numbered pieces act as the dates in the final solution, and of course need to be placed on the appropriate days. In the above December 2053 example, the blue piece marked “1” should go in the first row directly under Monday, since December 1st, 2053 is a Monday. Of course, all the remaining numbered tiles must fall in order and on their corresponding dates in the given month. When solving, it's important to note that the 1st of the month will always appear in the top row.

The puzzle itself is a 7×6-piece puzzle, with one square missing, so there are 41 pieces total. Since there are only 28 to 31 days in any given month, the white lettered tiles are used to fill up the otherwise empty spaces.

To make sure there's only one possible solution to the puzzle, these puzzles are placed in alphabetical order, reading left to right, then top to bottom. For example, if you're given a month that begins on a Tuesday, and is 30 days long, the goal would be to arrange the puzzle like this:



The A and B tiles take up the first two spaces, since the month starts on a Tuesday, and the letter tiles pick up from C, running in order through to K, after the last day of the month.

The puzzle will always give you the correct number of days for any given month. In the scrambled December puzzle up above, note that it has blue tiles marked 1 through 31, and white tiles lettered A through J. Compare that to the picture of the solved puzzle, which shows only 30 blue numbered tiles and lettered tiles marked A through K.

The puzzle also keeps track of how many moves you make, and how many seconds it's been since you moved your first tile.

Granted, you could cheat and refer to a perpetual calendar, which you can easily find online, but the real challenge is to do it WITHOUT referring to a calendar. One nice aspect of using your knowledge of the day for any date feat for this puzzle is that there's no time pressure. You can work out when the first day of the given month is, and then slide your first piece to start the clock.

The comments below the puzzle are open and I'm interested to hear how long it took you to solve. Leave your personal records, as well as any other comments or questions you have about it!

If you're curious, such puzzle calendars do exist in the real world, but I'm only aware of two sources. There's the mintpass calendar, which provides icons on the extra spaces for things such as date, birthdays, vacations, and so on. This one is far nicer than I am, as it provides a “HELP!” tab, which makes it easier to arrange the pieces as needed.

There's also the Puzzle Calendar by Yanko Design, in which the extra spaces are blank. However, the surface of all the sliding tiles, as well as the adjacent notepad, are made with a whiteboard surface, so you can add your own notes. The designers must really love the classic 15 puzzle, judging not only by their calendar, but this desk design, too.