A Python script to compute the odds of a game of Screw Your Neighbor (a.k.a. Ranter-Go-Round) by trying all possible combinations of deals.

SYourNeighbor.py

#! /usr/bin/env python

opponent_switch_threshold = 8
dealer_pulls_threshold = 10

def opponent_switches(dealer_card, opponent_card):
    """Given that the dealer and opponent have the given cards, returns
(dealer_win, opponent_win, tie) as the odds for each outcome if the opponent
switches with the dealer."""
    if dealer_card == 13:
        # Special rule if the dealer has a king. In this case he does not have
        # to switch. Technically this could result in a loss or a tie if the
        # opponent was switching with an ace or king, but we'll just call it a
        # loss for the opponent being so stupid.
        return (1.0, 0.0, 0.0)
    if dealer_card < opponent_card:
        # Dealer gave a lower card so the dealer's win is assured.
        return (1.0, 0.0, 0.0)
    else:
        dealer_win = 0
        opponent_win = 0
        tie = 0
        for new_card in xrange(2, 15):
            if dealer_card < new_card:
                dealer_win += 1.0/13.0
            elif dealer_card == new_card:
                tie += 1.0/13.0
            else:
                opponent_win += 1.0/13.0
        return (dealer_win, opponent_win, tie)

def dealer_pulls(opponent_card):
    """Given that the opponent has the given card, the opponent decided to keep
the card, and the dealer decided to pull a new card, returns
(dealer_win, opponent_win, tie) as the odds for each outcome."""
    dealer_win = 0
    opponent_win = 0
    tie = 0
    for new_card in xrange(2, 15):
        if new_card > opponent_card:
            dealer_win += 1.0/13.0
        elif new_card == opponent_card:
            tie += 1.0/13.0
        else:
            opponent_win += 1.0/13.0
    return (dealer_win, opponent_win, tie)

def opponent_keeps(dealer_card, opponent_card):
    """Given that the dealer and opponent have the given cards, returns
(dealer_win, opponent_win, tie) as the odds for each outcome if the opponent
keeps the card."""
    if dealer_card <= dealer_pulls_threshold:
        return dealer_pulls(opponent_card)
    else:
        return (float(dealer_card > opponent_card), \
                float(dealer_card < opponent_card), \
                float(dealer_card == opponent_card))

def odds_from_deal(dealer_card, opponent_card):
    """Given that the dealer and opponent have the given cards, returns
(dealer_win, opponent_win, tie) as the odds for each outcome using the
defined thresholds."""
    if opponent_card <= opponent_switch_threshold:
        return opponent_switches(dealer_card, opponent_card)
    else:
        return opponent_keeps(dealer_card, opponent_card)

def game_odds():
    """Trys all possible hands to determine odds for game using defined thresholds."""
    dealer_win = 0
    opponent_win = 0
    tie = 0
    for dealer_card in xrange(2,15):
        for opponent_card in xrange(2,15):
            (game_dealer_win, game_opponent_win, game_tie) = \
                odds_from_deal(dealer_card, opponent_card)
            dealer_win += game_dealer_win/169.0
            opponent_win += game_opponent_win/169.0
            tie += game_tie/169.0
    return (dealer_win, opponent_win, tie)

def try_all_thresholds():
    print "dealer pulls threshold,opponent switch threshold,dealer win,opponent win,tie"
    global dealer_pulls_threshold
    for dealer_pulls_threshold in xrange(5,13):
        global opponent_switch_threshold
        for opponent_switch_threshold in xrange(5,13):
            (dealer_win, opponent_win, tie) = game_odds()
            print "%d,%d,%f,%f,%f" % (dealer_pulls_threshold, opponent_switch_threshold, dealer_win, opponent_win, tie)

def try_all_deals():
    """Finds the odds for all possible deals."""
    print "dealer card,opponent card,dealer odds,opponent odds,tie odds"
    for dealer_card in xrange(2,15):
        for opponent_card in xrange(2,15):
            (dealer_odds, opponent_odds, tie_odds) = \
                odds_from_deal(dealer_card, opponent_card)
            print "%d,%d,%f,%f,%f" % (dealer_card, opponent_card, dealer_odds, opponent_odds, tie_odds)

if __name__ == '__main__':
    try_all_thresholds()
    #try_all_deals()