2 typo fix
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sed, 48 bytes

y/01234567890ABCDEFabcdef0123456789ABCDEFabcdef/fedcba9876543210543210/

Or 36 bytes if you only need to support one case.

sed, 48 bytes

y/01234567890ABCDEFabcdef/fedcba9876543210543210/

sed, 48 bytes

y/0123456789ABCDEFabcdef/fedcba9876543210543210/

Or 36 bytes if you only need to support one case.

1
source | link

sed, 48 bytes

y/01234567890ABCDEFabcdef/fedcba9876543210543210/