|Pathologically Eclectic Rubbish Lister|
Re^2: [OT] The statistics of hashing.by syphilis (Bishop)
|on Mar 31, 2012 at 23:55 UTC||Need Help??|
IIUC it's just (N/4294967296)**4
I believe the figure I should have provided is:
(1 - ((4294967295/4294967296) ** N)) ** 4
And if that's not right, I give up.
Update: The logic is simple. (Danger, Will Robinson ;-)
If you're picking numbers at random in the range (1 .. 4294967296), then the probability that the N+1th pick has already come up is:
1 minus the probability that it has *not* already come up
and the probability that it has *not* already come up is (4294967295/4294967296) ** N
So that gives us the
1 - ((4294967295/4294967296) ** N)
But because we're looking for the case where all *4* numbers have already come up, that probability needs to be raised to the 4th power ... which yields the final figure.