Pretty approachable once you see it as a counting problem.
Clarify the problem constraints and edge cases, then propose a solution using a hash map to store the custom order indices. Iterate through the custom order string, appending matching characters from the second string, then append any remaining characters. Discuss time and space complexity and potential optimizations.
Pro tip: Demonstrate awareness of Unicode and case sensitivity by asking whether the strings are ASCII or Unicode and if case matters. Also, mention that if the custom order is not a permutation of all characters, you can use a frequency map to handle duplicates efficiently.
Ask about character set (ASCII/Unicode), case sensitivity, and whether the custom order string contains all characters from the second string. Confirm that characters not in the order can be placed anywhere.
Use a hash map to map each character in the custom order to its index. Optionally, use a frequency map (or counting sort) for the second string to handle duplicates efficiently.
Iterate through the custom order string; for each character, append it to the result as many times as it appears in the second string (using the frequency map). Then append any remaining characters not in the custom order.
State that the time complexity is O(n + m) where n and m are the lengths of the strings, and space complexity is O(k) where k is the number of unique characters. Mention that this is optimal.
If the custom order is a permutation of all characters, you can sort using a custom comparator. For large alphabets, consider using an array if the character set is small (e.g., ASCII).
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.
This one tripped me up more than I expected for a follow-up.
Use a two-pointer technique to traverse the word and abbreviation simultaneously, handling digits by parsing the full number and skipping that many characters in the word. Validate that digits don't have leading zeros and that non-digit characters match exactly, ensuring the entire word is consumed.
Pro tip: Clarify edge cases upfront, such as empty strings, abbreviations with only digits, and numbers exceeding word length, to demonstrate thoroughness. Also, discuss time and space complexity (O(n) time, O(1) space) to show efficiency awareness.
Confirm with the interviewer the rules: no leading zeros, digits represent skipped characters, and non-digits must match. Discuss edge cases like empty strings, consecutive digits, and numbers larger than the word length.
Use two pointers, one for the word and one for the abbreviation, to traverse both strings. This allows efficient comparison and skipping without extra space.
When encountering a digit, parse the entire number (checking for leading zeros) and advance the word pointer by that count. Ensure the count doesn't exceed the remaining word length.
For non-digit characters, check if they match the current character in the word. If not, return false. Advance both pointers.
After traversal, ensure both pointers have reached the end of their respective strings. If not, the abbreviation is invalid.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.