You have two problems.

Replace my @less, @equal, @greater, @answer;

with

    my @less;
    my @equal;
    my @greater;
    my @answer;
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Replace unshift(@answer, @equals);

with    unshift(@answer, @equal);

That will result in a decreasing sort being returned.

I suggest you religiously specify use strict;. The problems were trivial to fix because they were specifically reported.