in reply to Re: Array problem
in thread Array problem

A slight alternative is to shuffle the indexes. 

my  @want = map{ 
    "@start[ $_, ( shuffle 0 .. $_-1, $_+1 .. $#start )[ 0 .. 2 ] ]"
} 0 .. $#start;

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Don't even need join anymore!

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Re^3: Array problem
by JavaFan (Canon) on Sep 27, 2008 at 09:54 UTC
    But neither are a good solution if the array is large: for each element, you're shuffling (almost) the entire array, just to get three elements. It makes for a quadratic solution, where a linear will do.
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        Just don't shuffle the entire array; stop if you have shuffled three elements (taking care you don't shuffle in the leading animal). 
        my @animals = qw [dog cat bird mouse rat snake horse cow
                  pig lizard lamb zebra lion elephant monkey];

my @scratch = @animals;

foreach my $animal (@animals) {
    for (my $j = @scratch - 1; $j >= @scratch - 3; $j --) {
        my $r = rand ($j + 1);
        @scratch[$j, $r] = @scratch[$r, $j];
        if ($scratch[$j] eq $animal) {
            my $r = rand ($j);
            @scratch[$j, $r] = @scratch[$r, $j];
        }
    }
    say "$animal @scratch[-3..-1]";
}

        [download]
        As one can see easily, the running time inside the main loop is independent of the size of the array, hence, O(1), making the entire program run in linear time.
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[d/l]
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