Asklemmy

43984 readers

823 users here now

A loosely moderated place to ask open-ended questions

Search asklemmy 🔍

If your post meets the following criteria, it's welcome here!

Open-ended question
Not offensive: at this point, we do not have the bandwidth to moderate overtly political discussions. Assume best intent and be excellent to each other.
Not regarding using or support for Lemmy: context, see the list of support communities and tools for finding communities below
Not ad nauseam inducing: please make sure it is a question that would be new to most members
An actual topic of discussion

Looking for support?

Looking for a community?

Lemmyverse: community search
sub.rehab: maps old subreddits to fediverse options, marks official as such
!lemmy411@lemmy.ca: a community for finding communities

~Icon~ ~by~ ~@Double_A@discuss.tchncs.de~

founded 5 years ago

MODERATORS

Is it possible for devices on an online group chat to toss a coin without trusting each other and the server? (discuss.tchncs.de)

submitted 6 months ago by smileyhead@discuss.tchncs.de to c/asklemmy@lemmy.ml

41 comments fedilink hide all child comments

you are viewing a single comment's thread
view the rest of the comments

[–] tetris11@lemmy.ml 4 points 6 months ago* (last edited 6 months ago) (3 children)

Everyone tosses three coins, and posts it in the chat
- If a player tosses three of the same, they have to toss again.
Everyone chooses the mode coin from their neighbour, and adds it to their stack
Each player, with 3+N coins, picks the mode coin in their own collection.
- Ideally: the player's own bias, is outweighed by the other player's biases.
The final coin is the mode of all players coins.

spoiler

from numpy import median
from pprint import pprint

players = {"p1" : [1,0,1],  ## playing fair
           "p2" : [0,0,1],  ## cheating
           "p3" : [1,1,0],  ## cheating
           "p4" : [1,1,0],  ## cheating
           "p5" : [0,0,1]}   ## playing fair
print("Initial rolls:")
pprint(players)

get_mode_coin = lambda x: int(median(x))
get_all_mode_coins = lambda x: [get_mode_coin(y) for y in x]

for play in players: ## Players add the mode coin from their neigbours
    players[play] = players[play] + get_all_mode_coins(players.values())
print("First picks:")
pprint(players)

for play in players: ## Players collapse their collections to mode
    players[play] = [get_mode_coin(players[play])]
print("Last modes:", players)

print("Final choice:", get_mode_coin([x for x in players.values()]))

Which as you can see, is no better than simply picking the median coin from the initial rolls. I thank you for wasting your time.

[–] smileyhead@discuss.tchncs.de 5 points 6 months ago

The last player (or server) still can choose a result, because it knows other tosses before making it's own.

[–] tetris11@lemmy.ml 2 points 6 months ago

Second attempt that factors in cheating.

spoiler

from numpy import median
from random import choice
from pprint import pprint

# Functions
get_mode_coin = lambda x: int(median(x))
def pick(player, wants):
    for neighbor in players:
        if player != neighbor:
            neighbor_purse = players[neighbor]["purse"]
            if wants:
                if wants in neighbor_purse: # Cheat
                    players[play]["purse"] = players[play]["purse"] + [wants]
                    continue
            players[play]["purse"] = players[play]["purse"] + [choice(neighbor_purse)]


# Main
players = {"p1" : {"purse": [1,0,1], "wants": False}, ## playing fair
           "p2" : {"purse": [0,0,1], "wants": 0}, ## cheating
           "p3" : {"purse": [1,1,0], "wants": 1}, ## cheating
           "p4" : {"purse": [1,1,0], "wants": 0}, ## cheating
           "p5" : {"purse": [0,0,1], "wants": False}}   ## playing fair

for play in players: ## Players pick a desired coin from each of their neighbours
    pick(play, players[play]["wants"])
print("First picks:")
pprint(players)

for play in players: ## Players collapse their collections to mode
    players[play] = [get_mode_coin(players[play]["purse"])]
print("Last modes:", players)

print("Final choice:", get_mode_coin([x for x in players.values()]))

So, my method doesn't work

[–] Dkarma@lemmy.world 2 points 6 months ago

First person gets a box showing heads tails. Once that is picked player 2 is shown a flip coin button. This isn't fucking hard except the sync between apps which you do via db on the back end.