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use strict;
use warnings;
...
    my ( $ary, $swaps ) = @_;
    printf "%2d swaps => %s\n", $swaps, join ' ', @$ary;
}

 3 swaps => Y0 Y1 Y2 X0 X1 X2
 4 swaps => Y0 Y1 Y2 Y3 X0 X1
...
 5 swaps => Y0 X0 X1 X2 X3 X4
16 swaps => Y0 Y1 Y2 Y3 Y4 Y5 Y6 Y7 X0 X1 X2 X3 X4 X5 X6 X7 X8 X9
16 swaps => Y0 Y1 Y2 Y3 Y4 Y5 Y6 Y7 Y8 Y9 X0 X1 X2 X3 X4 X5 X6 X7