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calculates winning trick probabilities in a simplified version of spades

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Octocat-spinner-32 lib
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Octocat-spinner-32 Rakefile

Spades Probability Calculations Build Status


Calculate the probabilities that the 2 of Clubs through Ace of Clubs, or any Spade will win the first trick in a simplified game of Spades.

The game is simplified in that card play for the first trick is completely automated:

  • if a player holds any clubs, they must play their lowest club
  • otherwise, the play may play any heart or diamond
  • if the player holds only spades, they must play one

The winner of the trick is the highest club or a spade.


The probabilities are calculated by taking a sample of N random decks containing M cards and playing through their first tricks.

# Run calculations with default (100 decks with 8 cards each)
$ rake odds

# 10000 decks containing 52 cards
$ rake odds DECKS=10_000 CARDS=52


The script is fully unit tested using minitest, run tests with rake or rake tests

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