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push @{ $h{$_} }, shift @B for (@A, reverse @A) x (@B / @A / 2),
                               (@A, reverse @A)[ 0 .. @B % (2 * @A) - 
+1 ];

for my $i (0 .. $#A) {
    $h{ $A[$i] } = [ @B[ grep { my $m = $_ % (2 * @A);
                                grep $_ == $m, $i, 2 * @A - $i - 1
                              } 0 .. $#B ] ];
}

my $iter = do {
    my ($pos, $step) = ('0E0', 1);
...
    }
};
push @{ $iter->() }, $_ for @B;