Random Permutations

[Jerzy Karczmarczuk]

Markus.Schnell@infineon.com wrote:
> Is there a library routine for random permutations?
> 
> I didn't find any and did a quick hack...

There are many algorithms.
One, quite natural and quite fast
(n log n; slower than linear, though...)

consists in:
1. Generate N random numbers r_k, say, uniform between 0 and 1.
2. Form N pairs (1,r_1), (2,r_2), (3, r_3) ... (N,r_n).
3. Sort this list/vector wrt the *secon* (random) number.
4. In the sorted list the firs values (indices) give you the result.

This is of course quite general, not restricted to any Haskell
peculiarities.

Jerzy Karczmarczuk