Klotski
Klotski is a sliding block puzzle thought to have originated in the early 20th century. The name may refer to a specific layout of ten blocks, or in a more global sense to refer to a whole group of similar sliding-block puzzles where the aim is to move a specific block to some predefined location.
Rules
Like other sliding-block puzzles, several different-sized block pieces are placed inside a box, which is generally in 4×5 size. Among the blocks, there is a special one which must be moved to a special area designated by the game board. The player is not allowed to remove blocks, and may only slide blocks horizontally and vertically. Common goals are to solve the puzzle with a minimum number of moves or in a minimum amount of time.Naming
The earliest known reference of the name Klotski originates from the computer version for Windows 3.1 by ZH Computing in 1991, which was also included in Microsoft Windows Entertainment Pack. The sliding puzzle had already been trademarked and sold under different names for decades, including Psychoteaze Square Root, Intreeg, and Ego Buster. There was no known widely used name for the category of sliding puzzles described before Klotski appeared.History
A significant precursor of the Klotzki puzzle is the 19th century 15-puzzle, where fifteen wooden squares had to be rearranged. The 15-puzzle enjoyed immense popularity in western countries during the late 19th century. Around this time, patents appeared for puzzles using differently shaped blocks. Henry Walton filed in 1893 for a sliding puzzle of identically-shaped rectangles, which according to Edward Hordern, is the first known sliding puzzle with rectangular blocks. Frank E. Moss filed in 1900 for a sliding puzzle of six squares and four rectangles, which is one of the first known occurrences of sliding puzzle with non-equal blocks.Lewis W. Hardy obtained copyright for a game named Pennant Puzzle in 1909, manufactured by OK Novelty Co., Chicago. The aim of this puzzle is identical to Klotski, and only its default blocks and arrangement are different. Hardy also filed in 1907, which is about a sliding-block puzzle similar to Pennant Puzzle, but with a slightly different combination of blocks and a different goal—not must only the largest block be moved to a specific location, but all of the other blocks must achieve a specific configuration as well. The patent was granted in 1912.
John Harold Fleming obtained patent for a puzzle in 1934 in England, with almost identical configuration as described in this page. The puzzle concerned has the same blocks and almost identical placement as forget-me-not, only that the unique horizontal 2×1 block is placed at the bottom instead of beneath the 2×2 block. The patent included a 79-step solution.
It is said that the game was already known in Japan around the 10th year of the Shōwa period, i.e. around 1935. The first account of occurrence of Klotski in China is in Shaanxi Province, where Lín Dé Kuān of Northwestern Polytechnical University noted children in a village playing a version of Klotski made with pieces of paper in 1938. One of the earliest books about standard Klotski was written by the Chinese professor Jiāng Cháng Yīng of Northwestern Polytechnical University in 1949，in his book 科学消遣. This book has been republished as
It is still unknown which version of the puzzle is the original. There are many confusing and conflicting claims, and several countries claim to be the ultimate origin of this game.
Solving
The minimum number of moves for the original puzzle is 81, which is verified by computer to be the absolute minimum for the default starting layout, if you consider sliding a single piece to any reachable position to be a single move.The first published 81-step solution is by Martin Gardner, in the February 1964 issue of Scientific American. In the article he discussed the following puzzles : Pennant Puzzle, L'Âne Rouge, Line Up the Quinties, Ma's Puzzle and a form of Stotts' Baby Tiger Puzzle.
For earliest published solutions, currently known is from Chinese educator Xǔ Chún Fǎng, in his book 數學漫談. His solution involves 100 steps.
Variation
There are several variations of this game, some with names specific to the culture of certain countries, some with different arrangement of blocks.It is still unknown whether these variations affected each other and how.
Other names
The following variations basically have the same layout and block arrangement, varying only in name, usually with some sort of story behind the names. It is completely unknown whether they share the same origin, though this is highly possible as they are identical to each other.Huarong Dao
Huarong Dao is the Chinese variation, based on a fictitious story in the historical novel Romance of the Three Kingdoms about the warlord Cao Cao retreating through Huarong Trail after his defeat at the Battle of Red Cliffs in the winter of 208/209 CE during the late Eastern Han Dynasty. He encountered an enemy general, Guan Yu, who was guarding the path and waiting for him. Guan Yu spared Cao Cao and allowed the latter to pass through Huarong Trail on account of the generous treatment he received from Cao in the past. The largest block in the game is named "Cao Cao".Daughter in the box
The Daughter in the Box wood puzzle depicts an "innocent young girl, who knows nothing of the world" trapped in a building. The largest piece is named "daughter", and other blocks are given names of other family members.Another Japanese variation uses the names of shogi pieces.
L'âne rouge
In France it is well known as L'âne rouge. It features a red donkey trying to escape a maze of fences and pens to get to its carrots. However, there is no known and documented record of its first existence in France.Khun Chang Khun Phaen
This is a variation from Thailand. Khun Phaen is a famous character in Thai legend, and the game is named after the epic poem Khun Chang Khun Phaen, in which the character is imprisoned. The game depicts Khun Phaen breaking out of the prison by overcoming its nine sentries.There is a slight difference between Khun Chang Khun Phaen and the standard layout – the two middle 1×1 blocks are moved to bottom. Other than that, all other blocks are the same. The origin of this variation is unknown.
Other block arrangements
In this context, the "basic" arrangement is assumed to be a 4×5 area laid out as follows:-- In the left-hand column, two 1×2 blocks with a 1×1 block beneath.
- In the right-hand column, two 1×2 blocks with a 1×1 block beneath.
- In the middle two columns, a 2×2 block at the top, with a horizontal 2×1 block beneath it, two 1×1 blocks beneath that, leaving a 2×1 empty space at the bottom.
Pennant Puzzle
Coded as C19 in Hordern classification, it is first copyrighted in 1909 by Lewis. W. Hardy in United States. Standard Trailer Co. has it copyrighted under the name Dad's Puzzler in 1926. Its arrangement is different:- The default location of all blocks are different from Klotski. For example, the largest square block is in upper left corner.
- It is in 4×5 area, with one 2×2, two 1×2, four 2×1, two 1×1 pieces.
- The exit of block is not at the bottom middle, but bottom left.