V (vim), 7 bytes

Óˆ± Ø^$ 

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Hexdump:

00000000: d388 b10a d85e 24 .....^$ 

Just two regexes. Explanation:

Ó " Remove all occurrences... ˆ " Any character ± " Followed by itself " This regex is actually just the compressed form of (.)\1 Ø " Count the number of matches ^$ " An empty line