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]";
}

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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.

In reply to Re^5: Array problem by JavaFan
in thread Array problem by Anonymous Monk

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