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  #26  
Old 11-23-2018, 06:28 PM
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Default Re: Need some help- organizing a work secret santa

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Originally Posted by JoeP View Post
So ... can we find an algorithm for assigning gifters and giftees which doesn't require retries (eg randomly pick, and retry the whole thing if anyone gets their own name), but which gives no information to any participant ie they only know their giftee and there is an equal probability of anyone being their gifter?
Doesn't the method at the end of the video do this?
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Old 11-23-2018, 06:48 PM
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Default Re: Need some help- organizing a work secret santa

I thought it shifted the "giving to" cards by one, so is identical to the method I suggested ... are you going to make me watch the video again?
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  #28  
Old 11-23-2018, 07:31 PM
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Default Re: Need some help- organizing a work secret santa

So which bit doesn't it do?

EDIT: Oh I think I get what you are saying. First you shuffle the pile randomly, then you cut and shift by one. So the match-ups are random since the numbers are in a random order.
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Old 11-23-2018, 11:03 PM
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Default Re: Need some help- organizing a work secret santa

They are almost random ... as cep pointed out, if you get told to gift to X you know that X is not giving to you, because the cards are in sequence.

It's something to do with cycles. Possibly sub-groups. Partitions of the set that don't include any partitions of size 1. :professor::thinkup:
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  #30  
Old 11-24-2018, 12:17 AM
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Default Re: Need some help- organizing a work secret santa

You know a little more than that: you know that no one in the whole group is giving a present to someone who is also their Santa. As Joe says there is only one cycle in the group. A truly random method should have the possibility of generating cycles of size 2, 3, .... up to N - 2 as well as N. For large N it's very unlikely that a random choice would generate one cycle of size N, but the shuffle-cut-shift method is certain to result in this otherwise unlikely outcome.

It's a similar problem to the ones you get in Ramsey theory (though this secret Santa one is different to the Ramsey theory ones, I think). Ramsey theory is notorious for generating proofs that the answer is less than a googleplex ( or even larger number ) when everyone believes that the actual answer is some small number, like 26, but can't prove that for certain - it gets mind-bogglingly complex for even quite small sets.
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Old 11-24-2018, 12:52 AM
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Default Re: Need some help- organizing a work secret santa

Ok, I see. I'm not sure many secret santa organizers would care about that bit of information, or they might consider it a feature.
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Old 11-24-2018, 02:14 AM
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Default Re: Need some help- organizing a work secret santa

Yes, I'm sure you're right. A more practical objection to the card write-shuffle-cut-shift method is that it's too much work. As well as doing the cards everyone has to write their "you are" number into a list so that their Santa can convert a number to a name - or the organizer has to do the conversion and then that organizer knows everyone's Santa including their own. Easier to just get everyone to write their names on scraps of paper and put them in a hat. You don't have to make everyone put the names they've pulled from the hat back in if the last person draws her own name out - just the last person and a few other volunteers. Not perfect but good enough and easy to do without making lots of work.
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  #33  
Old 11-24-2018, 10:21 AM
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Default Re: Need some help- organizing a work secret santa

All the more reason to let the computers take over. Insert relevant pop-culture quote here.
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Old 12-10-2018, 03:18 PM
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Old 12-10-2018, 07:47 PM
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  #36  
Old 01-08-2019, 05:41 PM
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Default Re: Need some help- organizing a work secret santa

No post-even briefing?
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Old 01-08-2019, 07:56 PM
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Default Re: Need some help- organizing a work secret santa

:ff: services are not currently required.
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