Dou Dizhu, or Fighting the Landlord, is a shedding game involving 3 players and a deck of cards plus 2 jokers with suits being irrelevant. Heuristically, one player is designated the “Landlord” and the others become the “Peasants”. The objective of the game is to be the first one to have no cards left. If the first person to have no cards left is part of the “Peasant” team, then all members of the “Peasant” team receive a reward (+1). If the “Landlord” wins, then only the “Landlord” receives a reward (+1).

The “Landlord” plays first by putting down a combination of cards. The next player, may pass or put down a higher combination of cards that beat the previous play.

Our implementation wraps RLCard and you can refer to its documentation for additional details. Please cite their work if you use this game in research.

Environment parameters

dou_dizhu.env(opponents_hand_visible=False)

opponents_hand_visible: Set to True to observe the entire observation space as described in Observation Space below. Setting it to False will remove any observation of the opponent’ hands and the observation space will only include planes 0, 2, 3, and 4.

Observation Space

The observation is a dictionary which contains an 'obs' element which is the usual RL observation described below, and an 'action_mask' which holds the legal moves, described in the Legal Actions Mask section.

The main Observation Space is encoded in 6 planes each with 5x15 entries. For each plane, the 5 rows represent 0, 1, 2, 3, or 4 cards of the same rank and the 15 columns represents all possible ranks (“3, 4, 5, 6, 7, 8, 9, 10, J, Q, K, A, 2, Black Joker, and Red Joker”). The meaning of each plane is described in the table below:

Encoding per Plane

Legal Actions Mask

The legal moves available to the current agent are found in the action_mask element of the dictionary observation. The action_mask is a binary vector where each index of the vector represents whether the action is legal or not. The action_mask will be all zeros for any agent except the one whos turn it is. Taking an illegal move ends the game with a reward of -1 for the illegally moving agent and a reward of 0 for all other agents.

Action Space

The raw size of the action space of Dou Dizhu is 27,472. Because of this, our implementation of Dou Dizhu abstracts the action space into 309 actions as shown below. Actions are abstracted by only focusing on the major combination and ignoring the kicker (e.g. a trio with single “4445” would be represented by “444*”). As a reminder, suits are irrelevant in Dou Dizhu.

For example, you would use action 0 to play a single “3” card or action 30 to play a trio of “5”.

Rewards

We modified the reward structure compared to RLCard. Instead of rewarding 0 to the losing player, we assigned a -1 reward to the losing agent.