Quoridor

The starting position for a 4-player game. In a 2 player game, green and orange are omitted.

Quoridor is played on a game board of 81 square spaces (9x9). Each player is represented by a pawn which begins at the center space of one edge of the board (in a two-player game, the pawns begin opposite each other). The objective is to be the first player to move their pawn to any space on the opposite side of the game board from which it begins.

The wall A is legal. Wall B is illegal because it does not face two spaces on each side.

The distinguishing characteristic of Quoridor is its twenty walls. Walls are flat two-space-wide pieces which can be placed in the groove that runs between the spaces. Walls block the path of all pawns, which must go around them. The walls are divided equally among the players at the start of the game, and once placed, cannot be moved or removed. On a turn, a player may either move their pawn, or, if possible, place a wall.

Legal pawn moves according to the location of the opponent and the walls.

Pawns can be moved to any space at a right angle (but not diagonally). If adjacent to another pawn, the pawn may jump over that pawn. If an adjacent pawn has a third pawn or a wall on the other side of it, the player may move to either space that is immediately adjacent (left or right) to the first pawn. Multiple pawns may not be jumped. Walls may not be jumped, including when moving laterally due to a pawn or wall being behind a jumped pawn.

Walls can be placed directly between two spaces, in any groove not already occupied by a wall. However, a wall may not be placed which cuts off the only remaining path of any pawn to the side of the board it must reach.

Quoridor is based on an earlier game, namely Blockade (also known as Cul-de-sac), invented by Philip Slater in 1975. Mirko Marchesi, a well-known famous game game designer, created another version of this game, called Pinko Pallino, which was published in 1995 by Epta games. Pinko Pallino was only for two players and was played on an 11×11 game board with a total of 42 walls and slightly different rules.[2]

After initial release, the game aroused interest. By 1997, the five largest game companies in the world: Gigamic (French), American Family Games, Inc., American Great American Trading Company, Mitra Game Company and Smart Chick bought the copyright of this game and released it to the world.^{[company names needs verification]} As a result, Quoridor quickly became popular all over the world. Many European educational institutions (e.g. MINDLAB) have also selected Quoridor as teaching aids and brought them into the classroom.

History of the Notation(s): There isn't a notation provided by Gigamic. In 2005, Lisa Glendenning's thesis[3] proposed a reasonable notation. From the first players view the board is labeled a to i (right to left) in alphabetical order, and 9 to 1 (bottom to top). Later in the years algebraic chess notation influenced this notation and now a similar notation is used.

Each square gets a unique letter-number designation. Columns are labeled a through i from player 1's left and rows are numbered 1 through 9 from player 2's side to player 1's side. From player 1's perspective the far left square is labeled as a1. A move is recorded as the column followed by the row as in e2. For example: player 1's pawn starts on e1 and player 2's pawn starts on e9. See the image here.

Each pawn move is defined by the new square occupied by the pawn. For example, if player 1 moves from square e1 to e2, player 1’s move is denoted as e2.

Each wall move is defined by the square directly to the northwest of the wall center from player 1's perspective, as well as an orientation designation. For example: a vertical wall between columns e and f and spanning rows 3 and 4 would be given the designation e3v.

Every wall touches four squares. A wall move is denoted by the closest square to a1, and the direction (horizontal or vertical).

Games are notated as they are in chess: by the move number, player 1's move, and player 2's move. For example, a game might start with each player moving their pawn towards the center:

1. e2 e8

2. e3 e7

Then the players might add walls to lengthen the other player's path:

3. e6h e3h

and the game continues.

4. __ __

Forsyth–Edwards Notation (FEN) can be adapted for describing a particular board position of Quoridor. Optimally, it follows the pattern below.

H:[horizontal walls] / V:[vertical walls] / [position of player pawns (from 1 to 2 (or 4))] / [number of walls in the players hands (from 1 to 2 or 4)] / [whose turn it is]

There is an example from a 2 player game:

H:d4f4e7 / V:a2a8 / e4 e6 / 7 8 / 2

A game can be divided into 3 phases, namely opening, middle game, and endgame. The first 5-7 moves can be considered as the opening phase. A typical mid-game consist ~10 moves. The endgame starts when one of the players have less than 3 pieces.

Between games common patterns can be seen. The openings can be divided into two categories, orthodox and unorthodox openings. In orthodox openings the goal is to advance ones pawn to the center. Unorthodox openings are not common and uses 2 or more wall moves before ones pawn reaches e4 or e6.

In 1997, the game was awarded the Mensa Select, a prize given to five board games by the American Mensa every year. It was also by Games Magazine named Game of the Year 1998.

Quoridor: Awards[4]
Year	Awards	Country	Result
1996	Special mention at the award Best of Show (for Pinko Pallino)[5] by Lucca Games	Italy
1997	Mensa Select	United States	Won
	Best Bet of the Toy Testing Council	Canada	Won
	Prix d’Excellence des Consommateurs (Consumer’s Toy Award)		Won
	Gold Award by Parents’ Choice	Germany	Won
	Spelgut		Won
	Grand Prix du Jouet[6]	France	Won
	Toy Award	Belgium	Won
1998	Games 100 Selection by Games Magazine	United States	Won
	Game of the year[7] by Games Magazine		Won

The Children's version of the game Quoridor Kid won 4 awards.

Quoridor Kid: Awards[8]
Year	Awards	Country	Result
2006	Creative Child Magazine Preferred choice award	United States	Won
2008	Best Children’s Game by Boardgames Australia	Australia	Won
2009	Best children’s game	Finland	Won
		Sweden	Won

There are different board sizes of the game: Pocket < Mini < Regular < Deluxe < Giant

• Quoridor Pocket: A portable version. The regular version of the board and top is made of wood, but the "pocket" is made of plastic.
• Quoridor Mini / Quoridor Travel: The smallest version of the game.
• Quoridor Deluxe: A carved version of wood. The game board is not painted and colored, and the grain remains. Size of the board is one size larger than the regular version. The color of the pieces has also been changed.
• Quoridor Giant: The design is the same as the normal version, but the size is about 4 times bigger.

Quoridor Kid: In 2004 Gigamic released the Children's version. The number of squares on the board is 7x7 squares, which is one size smaller than the regular version, and the number of walls is 16 (for 2 players, each player gets 8 walls; for 4 players, 4 each). Other rules are the same. The board is round and yellow, where classic figures are replaced with a mice. The top is in the shape of a mouse, and a cheese top is placed in the back of the row on the other side, adding the theme of "a mouse is trying to reach the cheese."

Mindsports Olympiad: As part of the Mindsports Olympiad 2020, Quridor was played.[9]

Pentamind World Championship: In 2018, Quoridor was played among 5 games in the Pentamind tournament.[10]

MINDLAB: Kids between the ages 9-12 can participate in this yearly tournament.

Quoridor has a relatively large complexity, the number of valid positions in the game (state space) is ${\displaystyle 10^{42}}$. The number of nodes on the game tree respectively is ${\displaystyle 10^{42}}$ and ${\displaystyle 10^{162}}$. In each position, there are an average of ${\displaystyle 60}$ valid moves. For comparison these numbers are in chess ${\displaystyle 10^{47}}$, ${\displaystyle 10^{123}}$ and ${\displaystyle 35}$, respectively.

In the starting state there are ${\displaystyle 128}$ positions of valid walls and ${\displaystyle 4}$ moves so the game has a total of ${\displaystyle 132}$ branches.

There are a total of ${\displaystyle 1,375,968,129,062,134,174,771\approx 1.3\times 10^{21}}$ possible positions of the game. [11]

A digital chess clock

Time control

In competition, Quoridor games are played with a time control. If a player's time runs out before the game is completed, the game is automatically lost.

Time can be controlled controlled using a chess clock that has two displays, one for each player's remaining time. Analog chess clocks have been largely replaced by digital clocks, which allow for time controls with increments.

• Blockade (board game)

• Mertens, P. J. C. (June 21, 2006). A Quoridor-playing Agent (PDF) (B.Sc. thesis). Maastricht University.
• Lisa Glendenning's thesis
• Q. McDermid, A. Patil, and T. Raguimov's paper
• G. Tsur, Y. Segev (unknown year) Quoridor Agent (PDF) Hebrew University of Jerusalem.