My first instinct was to just loop and scan repeatedly until nothing changed, which works but is obviously O(n^2) and they pushed back immediately when I mentioned the string could be up to 100k chars.
Clarify the problem and edge cases, then propose an efficient stack-based solution that processes the string in one pass. Explain how the stack naturally handles adjacent duplicates and demonstrate with a small example before coding.
Pro tip: Mention that a stack is ideal because it mirrors the recursive removal process, and note that the solution runs in O(n) time and O(n) space. Also, discuss how to handle the final string construction efficiently.
Restate the problem in your own words and confirm details: only lowercase letters, remove adjacent identical pairs repeatedly until no such pairs remain. Ask clarifying questions if needed.
Recognize that a stack can efficiently simulate the removal process. As you iterate through the string, compare the current character with the top of the stack; if they match, pop; otherwise, push.
Trace the algorithm on a small example like 'abbaca' to demonstrate correctness and build intuition. Show how the stack evolves and the final result is obtained.
State that the time complexity is O(n) because each character is pushed and popped at most once, and space complexity is O(n) for the stack in the worst case.
Write clean code, handle edge cases (empty string, no removals, all removals), and test with a few examples. Discuss potential optimizations or alternative approaches if relevant.
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