D:\Perl\test>perl
use strict;
use warnings;

my %h; @h{'a'..'j'} = 0..9;
print %h, $/;

my ($min,$max) = (keys %h);
($min,$max) = ( $h{$min} < $h{$_} ? $min : $_, $h{$max} > $h{$_} ? $max : $_ ) for keys %h;

@h{$min,$max} = @h{$max,$min};
print %h, $/;

^Z
a0b1c2d3e4f5g6h7i8j9
a9b1c2d3e4f5g6h7i8j0