Mahjong solitaire is a sub-genre of puzzle games that utilize mahjong tiles and are generally played by a single player (similar to other "solitaire" games, such as card solitaire). As the game name is generally shortened to Mahjong (or Mah-Jongg), it is often confused with traditional mahjong. It is sometimes known in Japan as Shanghai, in reference to the game series of the same name.
The goal of most games of mahjong solitaire is to remove all tiles from the board by matching pairs of "open tiles" (also known as "free tiles" or "exposed tiles"). A tile is considered an "open tile" if it has no tile above it and has one of its longer sides (generally horizontal) unobstructed by another tile. While the tile setup is randomized, each game usually has various tile "formations", the most common of which is the five-layer "Turtle" (named for its resemblance to an upright shelled turtle). Similar to most other solitaire games, the board can be made unwinnable if no valid pairs can be found, with the possibility of players beginning the game with an unwinnable state.
Most variations use the entire set of 144 mahjong tiles, with four copies of the nine Character ("manzu") tiles, nine Dot ("pinzu") tiles, nine Bamboo ("souzu") tiles, four Wind ("kazehai") tiles, and three Dragon ("sangenpai") Tiles, and one copy of the four Season ("kisetsuhai") tiles and four Flower ("hanahai") tiles. The Season and Flower tiles serve as "wildcards", with all Season tiles compatible with each-other and all Flower tiles compatible with each-other.
The origins of mahjong solitaire as a tabletop game are currently unknown. As a computerized game, it originates with the 1981 game Mah-Jongg, developed by Brodie Lockard for the PLATO system. The first mainstream adaptation of the game was the 1986 Activision game Shanghai, which spawned a long-running series (notable for its many different variants, both single-player and multiplayer).
Due to the sub-genre's popularity, especially with touch-screen devices, it is considered one of the main pillars of the "casual game" genre.
A Japanese variant of the game, known as either Nikakudori (loosely translated to "Two-Angle Take") or Shisen-shou (loosely translated to "Sichuan Province", also commonly referred to as Shisen-Sho or Shisen Sho), changes the way the board is presented while presenting a new rule:
- The layout is now unstacked, with the most common version arranging the tiles to form a closed rectangle (usually 17×8). Some variants allow layouts of different shapes and sizes. Some games, such as Rong Rong, include stacked tiles with a rule that tiles can only be matched on the same layer.
- All tiles are considered "open tiles", although matching tiles can only be removed from the board if they follow the rule of "nikakudori" (or "two-angle take"): when determining if two matching tiles can be removed, a path of straight lines (horizontal and vertical) must be imagined between them so that no line touches any other tile and the path must form less than three right angles.
Some computerized variants also have a "gravity" setting, in which removed tiles causes all tiles that are vertically above them to be moved downward (similar to the puzzle SameGame).
The origins of nikakudori as a tabletop game are currently unknown. As a computerized game, it is believed to originate with the 1989 Tamtex arcade game Shisen-shou: Joshiryou-hen - Match It.