[Bug][3P] The Dora indicator tile appears more than 4 times

[shinkuan]

Content

Description
During 3P (3-player) simulated matches, I noticed an anomaly where a specific tile occasionally appears more than four times. After carefully analyzing the board, I discovered that these excess tiles always happen to be the Dora indicator tile.

Expected Behavior
Any specific tile should have a strict maximum of four copies in the entire tile set, regardless of whether it is selected as a Dora indicator.

Actual Behavior
The first Dora indicator tile appears more than four times in the game (e.g., a total of 5 copies).

Screenshots / Logs

Environment

• Mode: 3P Simulation
• Version: v0.4.6

[shinkuan]

I tried to make a reproducible script for this bug, please run it with the attached files below.

player0_output.log
player1_output.log
player2_output.log

import os
import json
from riichienv import RiichiEnv, Action3P, GameRule
from riichienv.convert import *
from IPython.display import HTML


# ===== Agent that replays the same game using the logs =====
class PreloadAgent:
    def __init__(self, player_id: int):
        self.player_id = player_id
        log_output_file = f"player{player_id}_output.log"
        with open(log_output_file, "r") as f:
            self.responses = [line.strip() for line in f.readlines()]
        self.response_index = 0

    def act(self, obs) -> Action3P:
        resp = self.responses[self.response_index]
        self.response_index += 1
        action = obs.select_action_from_mjai(resp)
        assert action is not None, "Mortal must return a legal action"
        return action

# ===== Main simulation =====
env = RiichiEnv(game_mode="3p-red-half", rule=GameRule.default_tenhou(), seed=27)
agents = {pid: PreloadAgent(pid) for pid in range(3)}
obs_dict = env.reset()

try:
    while not env.done():
        actions = {pid: agents[pid].act(obs) for pid, obs in obs_dict.items()}
        obs_dict = env.step(actions)
except:
    viewer = env.get_viewer()
    html: HTML = viewer.show()  # show() accepts optional display parameters
    viewer.summary()            # list of round info dicts (bakaze, kyoku, honba, oya, scores)
    with open("debug_output.html", "w") as f:
        f.write(html.data)
    with open("debug_summary.json", "w") as f:
        for mjai_event in env.mjai_log:
            f.write(json.dumps(mjai_event, separators=(",", ":")) + "\n")

# ===== Tile counter for overflow detection =====
tiles = [
    "1m", "2m", "3m", "4m", "5m", "6m", "7m", "8m", "9m",
    "1p", "2p", "3p", "4p", "5p", "6p", "7p", "8p", "9p",
    "1s", "2s", "3s", "4s", "5s", "6s", "7s", "8s", "9s",
    "E", "S", "W", "N", "P", "F", "C"
]
tile_counter = [0] * 34

for mjai_event in env.mjai_log:
    print(f"event: {mjai_event}")
    # Pai counter
    match mjai_event['type']:
        case 'start_kyoku':
            tile_counter = [0] * 34  # Reset tile counter at the start of each kyoku
            for tehai in mjai_event['tehais']:
                for pai in tehai:
                    if len(pai) == 3:  # 5mr / 5pr / 5sr
                        pai = pai[:2]
                    tile_counter[tiles.index(pai)] += 1

            pai = mjai_event['dora_marker']
            print(f"Dora marker: {pai}")
            if len(pai) == 3:  # 5mr / 5pr / 5sr
                pai = pai[:2]
            tile_counter[tiles.index(pai)] += 1

        case 'tsumo':
            pai = mjai_event['pai']
            if len(pai) == 3:  # 5mr / 5pr / 5sr
                pai = pai[:2]
            tile_counter[tiles.index(pai)] += 1

        case 'dora':
            pai = mjai_event['dora_marker']
            print(f"Dora marker: {pai}")
            if len(pai) == 3:  # 5mr / 5pr / 5sr
                pai = pai[:2]
            tile_counter[tiles.index(pai)] += 1

        case _:
            pass

    if any(count > 4 for count in tile_counter):
        print(f"Overflow detected!\nOverflow tile: {tiles[tile_counter.index(max(tile_counter))]}\nTile counts: {dict(zip(tiles, tile_counter))}")
        raise AssertionError("Tile count overflow detected!")

Expected output:

...
event: {'actor': 1, 'pai': 'E', 'type': 'tsumo'}
Overflow detected!
Overflow tile: E
Tile counts: {'1m': 2, '2m': 0, '3m': 0, '4m': 0, '5m': 0, '6m': 0, '7m': 0, '8m': 0, '9m': 4, '1p': 4, '2p': 2, '3p': 4, '4p': 4, '5p': 3, '6p': 3, '7p': 4, '8p': 3, '9p': 4, '1s': 3, '2s': 3, '3s': 2, '4s': 3, '5s': 2, '6s': 3, '7s': 4, '8s': 2, '9s': 3, 'E': 5, 'S': 3, 'W': 3, 'N': 4, 'P': 3, 'F': 4, 'C': 3}
Traceback (most recent call last):
  File "find_overflow.py", line 88, in <module>
    raise AssertionError("Tile count overflow detected!")
AssertionError: Tile count overflow detected!

[smly]

Thank you for the detailed reproduction script and log files, @shinkuan!

The root cause identified. The 3P shuffle() dead wall layout only allocated 4 rinshan tiles (same as 4P), but 3P mahjong requires 8 rinshan tiles because kita (north extraction) also draws from the dead wall. Rinshan draws always used tiles.remove(0), so after the 4 dedicated rinshan tiles were exhausted, the 5th+ draws consumed dora/ura indicator tiles from positions tiles[4..14]. This caused the same physical tile to appear both as a dora indicator and in a player's hand, making a tile type appear more than 4 times.

This issue is specific to 3P mode. In 4P mode the maximum rinshan draws is 4 (kan only, no kita), which exactly matches the dedicated rinshan slots, so the overflow never occurs.

Planned Fix

1. Correct the 3P dead wall layout: expand rinshan area from 4 to 8 tiles, move dora indicator positions from tiles[4..14] to tiles[8..18]
2. Update the exhaustive draw threshold from tiles.len() <= 14 to tiles.len() <= 18 (DEAD_WALL_SIZE_3P)

(Updated) The exhaustive draw threshold remains at 14. The 3P dead wall is 7 stacks (14 tiles): 4 stacks (8 tiles) for rinshan draws + 3 stacks (6 tiles) for dora indicator stacks 1-3. Dora indicator stacks 4-5 (2 stacks = 4 tiles) overflow into the live-wall area.

I have identified the root cause and prepared the fix diff. Since MjSoul game records define the full wall including rinshan tiles, I will create a validation script using those records to verify that rinshan draws are now correct.

[smly]

Fixed in #186. Expanded rinshan area to 8 tiles and refactored exhaustion checks to use a drawable_count counter. Validated against 1,814 MjSoul 3P kyoku (60,387 draws, 0 failures). I also confirmed with your reproduction script and log files (seed=27) that the tile overflow no longer occurs. All tile counts stay within the expected maximum of 4.

Thank you for the detailed bug report and reproduction script!