My first instinct was to use regex and I immediately talked myself out of it, which was probably the right call.
Use a two-pointer technique to traverse both strings simultaneously, parsing numbers in the abbreviation and expanding them to skip characters in the target string. Handle edge cases like leading zeros, numbers exceeding remaining length, and ensure both strings are fully consumed.
Pro tip: Clarify whether the abbreviation can contain numbers that represent substrings of length zero or with leading zeros, as these are common pitfalls. Also, discuss how you would test your solution with edge cases like empty strings and large numbers.
Ask the interviewer about constraints: can the abbreviation contain leading zeros? Can numbers be zero? Are both strings non-empty? This ensures you handle all cases correctly.
Use pointers i for abbreviation and j for target. Iterate through the abbreviation: if the character is a digit, parse the full number and advance j by that amount; if it's a letter, check it matches target[j] and advance both.
When encountering a digit, accumulate the number. Reject leading zeros (unless the number is exactly '0', which is invalid). After parsing, ensure the number doesn't exceed the remaining length of the target string.
After the loop, both pointers must have reached the end of their respective strings. If not, the abbreviation is invalid.
Walk through examples like 'i18n' vs 'internationalization' and 'i18n' vs 'interpolation'. Also test edge cases: empty strings, abbreviation with only numbers, and numbers that are too large.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.