find-invalid-ip-addresses.sql

# Time:  O(nlogn)
# Space: O(n)

# regular expression
SELECT ip,
       COUNT(*) AS invalid_count
FROM logs
WHERE ip NOT REGEXP "^((25[0-5]|2[0-4][0-9]|1[0-9][0-9]|[1-9][0-9]|[0-9])(\\.(25[0-5]|2[0-4][0-9]|1[0-9][0-9]|[1-9][0-9]|[0-9])){3})$"
GROUP BY 1
ORDER BY 2 DESC, 1 DESC;