Riddle of the Day is a new feature on Málstaður, Miðeind's language technology website. It is a crossword puzzle that is published daily, at midnight. A partially completed Scrabble puzzle is provided along with a rack of 7 letters — and the player's task is to find the highest-scoring possible move on the board, i.e., a word that can be formed horizontally or vertically and connects to a word that is already there.

The thermometer on the right side of the image shows words the player has already tried to play, ranging from AR (which scored 3 points) up to ÞÖKUR (which scored 67 points). However, the player has not yet found the best possible move, which scores 69 points (the number in the green circle at the top of the thermometer). Can you spot it? The seven letters on the rack are ÞKURMRI.

The top right shows that this is the puzzle for February 2nd, but it's possible to go back and view older puzzles—and look up their solutions, if the player hasn't already found them. The number “98” indicates that 98 players solved the puzzle on the day it was active.

Players compete both to find the solution and to do so quickly. A leaderboard shows the top 50 players, in chronological order within each score, so the person who is first to solve the puzzle and find the highest-scoring move is at the top of the leaderboard.

The Puzzle of the Day is partly based on the popular Netskrafl (Online Scrabble), for which over 40,000 Icelanders have registered to play at some point in the 10 years since the game was first released on the web.

The idea for the Puzzle of the Day originated in a so-called hackathon within Miðeind. Miðeind regularly holds internal hackathons where staff split into teams and have about a week to rapidly turn an idea into a prototype. At the end of the hackathon, a presentation is held where the teams show their results and admire each other's ingenuity. In the case of the Puzzle of the Day, the hackathon had a gaming theme; all sorts of ideas for games and fun activities related to Icelandic and Icelandic culture were developed and presented.

After the hackathon, it was decided to fully develop the Puzzle of the Day. The prototype was discarded, and a new system architecture was designed that intertwined with the migration of Netskrafl to Málstaður.

The core of the Puzzle of the Day is Miðeind's Scrabble engine, which is written in the Go programming language and is extremely fast. It utilizes parallel processing on modern multi-core processors. This means the engine initiates multiple processes (specifically 30, one for each row and column of the Scrabble board) that work simultaneously to find possible moves on a given board.

For each day's puzzle, the Scrabble engine is made to play a number of games against itself until a promising board position emerges. Such a position has, among others, the following characteristics:

• There must be one and only one best solution word.

• The more the solution word stands out from other possible moves, the better.

• However, the solution word must not be too obvious, for example, by spanning two triple-word-score squares and thus being vastly better than any other possible word.

• The solution word must be reasonably common in Icelandic text.

• The word must not be too short; the longer, the better.

• The best possible score must be at least 30 points.

Once 100 promising puzzles have been collected for each day, the best one is selected. All the processing and filtering involved means that it takes several minutes of computation on a powerful computer—despite the Scrabble engine being very fast—to prepare ~30 puzzles for a whole month of the Puzzle of the Day.

The daily puzzles are usually calculated and prepared in advance and stored in a database until they are published. But the code can also generate them on the fly if needed.

The Puzzle of the Day has been very well received. A great race often begins among the country's most skilled crossword puzzle whizzes just after midnight and in the early morning to get onto the Top 50 leaderboard, let alone into the top three spots, which award gold, silver, and bronze medals.

The puzzle is open to everyone and free of charge. The only requirement to participate is to be logged in to Málstaður. Try the Puzzle of the Day at gatadagsins.is!

P.S. The solution to the puzzle on February 2nd is ÞÖKUM (instead of ÞÖKUR), which scores 69 points!