My first move was reaching for a frequency map which was completely wrong for this.
Use a two-pointer technique to traverse both strings simultaneously, advancing the pointer for the first string always and the pointer for the second string only when characters match. If a character in the first string repeats, ensure the second string has at least one occurrence before moving on. This approach runs in O(n) time and O(1) space.
Pro tip: Clarify edge cases upfront, such as empty strings or when the second string is longer than the first, and mention that the solution should handle Unicode characters if relevant. Also, discuss potential follow-ups like handling multiple long-pressed keys or returning the original string.
Restate the problem in your own words and ask clarifying questions about input constraints, character sets, and expected behavior for edge cases like empty strings or when the second string is longer.
Explain that you'll use two pointers, i for the first string and j for the second. Iterate through the first string, and when characters match, advance j; otherwise, ensure the current character in the first string is a repeat of the previous one.
Trace the algorithm on examples like 'leet' and 'leeeet' to show how it works, and also on a negative example like 'leet' and 'let' to demonstrate early termination.
State that the time complexity is O(n) and space is O(1). Mention that no further optimization is needed, but you could discuss alternative approaches like run-length encoding if the interviewer asks.
Explicitly check edge cases: if the second string is longer, return false; if the first string is empty, return true only if the second is also empty. Suggest writing unit tests for these scenarios.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.