Re^2: getting random number 8 times never the same

[JavaFan]

For long lists, that isn't more efficient than shuffling. Shuffling means going through the list once, swapping each element. Splicing means going through (on average) half the list in each iteration moving the element one to the left.

Splicing a random element out of an array takes on average linear time.

[BrowserUk]

For long lists, that isn't more efficient than shuffling.

Regardless of the length of the list, which is quicker depends upon the ratio of picks.

...for a small number of picks, Ie. If the ratio of picks to list size is less than ~15%, spliceing is quicker than shuffling the whole list:

#! perl -slw
use strict;
use List::Util qw[ shuffle ];
use Benchmark qw[ cmpthese ];

our $N //= 20;
our $S //= 8;
our @nums = 0 .. $N;

cmpthese -1, {
   shuffle => q[ my @s = ( shuffle @nums )[ 0 .. $S-1 ]; ],
   splice  => q[ my @s = map splice( @nums, rand( @nums ), 1 ), 1 .. $
+S; ],
};

__END__
c:\test>868601 -N=10 -S=2
            Rate shuffle  splice
shuffle 894654/s      --    -10%
splice  993686/s     11%      --

c:\test>868601 -N=10 -S=3
            Rate  splice shuffle
splice  769417/s      --     -9%
shuffle 844675/s     10%      --

c:\test>868601 -N=100 -S=15
            Rate shuffle  splice
shuffle 196571/s      --     -5%
splice  207873/s      6%      --

c:\test>868601 -N=100 -S=17
            Rate  splice shuffle
splice  186995/s      --     -3%
shuffle 192359/s      3%      --

c:\test>868601 -N=1000 -S=169
           Rate shuffle  splice
shuffle 19552/s      --     -2%
splice  19968/s      2%      --

c:\test>868601 -N=1000 -S=170
           Rate  splice shuffle
splice  20274/s      --     -1%
shuffle 20569/s      1%      --

c:\test>868601 -N=10000 -S=1998
          Rate shuffle  splice
shuffle 1578/s      --     -6%
splice  1674/s      6%      --

c:\test>868601 -N=10000 -S=1999
          Rate  splice shuffle
splice  1601/s      --     -1%
shuffle 1625/s      2%      --