In Vim how can I search and replace every other match?

Question

Say I have the following file

Answer 1

I'd do it with a macro:

qv            start recording in register v
/"bar"/e  search for "bar" and position the cursor at the end of the match
i1       insert 1 before the cursor and go back to normal mode
n             jump to next match
q             stop recording

After that, do {count}@v.