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### Carcassonne

The Game

Carcassonne is a tile-laying game. The objective of the game is to build regions and to occupy regions. When a region is completed, the players with the most followers in the region receive an appropriate number of points. The game is over when there are no more tiles available. The player with the most points wins.

Note: This version of Carcassonne is mostly simpler than the original but has been changed at a few points to drive home some points on the interaction among software components. You may want to consult the rules for the original game and even play it to get a feeling for the process but beware that the rules differ.

The Tiles
Every tile depicts some theme: an abbey, a castle, a road, or a combination of these. Here are three examples:

The leftmost tile with the red boundary is the unique starter tile. At the northern end it depicts a fragment of a castle, the white line running from left to right is a road fragment. The center tile is an abbey. The rightmost tile depicts the fragment of a castle that borders the northern as well as the eastern side of the tile.

Before you read on, take a look at the collection of all tiles.

Turns, Part I
At each turn, a player obtains a tile at random from a heap of tiles that are arranged face-down, turns it over, and adds it at some matching place to the map. Matching means that the border of each neighboring tile is the same as the border of the newly placed tile. Furthermore, the newly placed tile must share a border with at least one existing tile. To create a match, a player may rotate a tile by 90, 180, or 270 degrees.

Placing a tile may thus involve

1. one neighboring tile:
 0 1 0 1
Here the player placed tile 1 without rotating it to the south of the starter tile, matching grass to grass.
2. two neighboring tiles:
 -1 0 0 1
This time the player rotated tile 2 by 270 degrees into the (-1,0) spot. On its eastern border the tile matches two roads (with grass); on the southern border it matches grass.
3. three neighboring tiles:
4.  -1 0 -1 0 1
If the player places the tile into spot (-1,0) in this situation, the turn requires three matches for the tile: on its southern, eastern, and northern border.
5. or even four neighbors. Make an example where placing a tile requires four matches.

Over the course of a game, this map of tiles evolves. The map is usually not densely connected, like the four examples might suggest. The ultimate shape depends on the strategy of the players and how they operate to build regions.

Note: If it is impossible to add a tile to the map, the player may return the tile to the heap and pick up another tile.

Regions
A region is a collection of connected tiles with the same theme (roads, castles) or an abbey with its surrounding neighbors. A region is complete if it meets the following conditions:
• A road is complete if it has an end piece at either end. End pieces are: farms; forks in the road; and castles and abbeys:
2:    6:    7:    19:    23:    24:

Example:

• An abbey is complete if it is surrounded by eight (8) pieces.

Example:

• A castle is complete if it its walls form a continuous line.

Example:

Turns, Part II
After placing a piece, a player may also place a follower on a region if the region is incomplete and if no other follower already occupies the region. Placing a follower is optional and should follow strategic considerations because a player has only seven followers.

When the placement of a tile completes a region, the follower(s) are immediately returned to their respective player. This implies that the player who just placed the tile may use a returned follower to end his turn.

It is permissible to connect two distinct regions with followers, and this kind of move is indeed an important part of the game.

Scoring
Players receive points when regions are completed. If a region is populated by the followers of several players, the player with the most followers in the region receives the points. Sometimes several players have the same number of followers in the region. In this case all players with the highest number of followers receive the points.

Points correspond to the number of pieces in a region. Thus a completed abbey always yields nine (9) points. A completed road produces as many points as there are participating tiles, including the end pieces. Each castle tile accounts for two (2) points, unless it also contains a flag, in which case it accounts for four (4) points.

The End
A game consists of 70 to 75 turns, depending on the number of players. That is, there are 70 to 75 cards (1 through 24) in the heap. You may assume that the chances of picking any one of the 24 cards are the same.

At the end of the game, players receive additional points for followers that occupy abbeys. The score for an incomplete abbey region consists of one point for the abbey tile plus the number of tiles that touch the abbey, i.e., a player may obtain up to eight (8) points for an abbey at the end of the game. The followers on incomplete roads and incomplete castles are ignored.

Bibliography
Dan Becker, Carcassonne, Game Review.

 last updated on Tue Jun 9 22:03:19 EDT 2009 generated with PLT Scheme