how to write only one pattern to exchange two strings in two-ways in vim

Question

xxx <=> zzz

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Original text:

xxxyyyzzz

Run command:

:s/???/???/

It becomes:

zzzyyyxxx

Run the same command above:

:s/???/???/

Back to the original text:

xxxyyyzzz

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just like toggle case(~)

aBCdeFg <=> AbcDEfG

Answer 1

Take a look at this: Can I substitute multiple items in a single regular expression in VIM or Perl?

Answer 2

Try this:

:s/(...)(yyy)(...)/\3\2\1/