Knew the trick immediately: count character frequencies, at most one can be odd.
First, clarify that a palindrome can have at most one character with an odd frequency. Then, count the frequency of each character and check if the number of odd counts is 0 or 1. This can be done in O(n) time and O(1) space using a bitmask or a frequency array.
Pro tip: Mention that you can optimize space by using a bitmask to track odd counts, toggling bits as you iterate. This shows you think about efficiency and low-level optimizations, which is valued at Meta.
Ask if the string contains only lowercase letters or any characters, and confirm that a palindrome reads the same forwards and backwards.
Explain that a palindrome can have at most one character with an odd frequency. All other characters must appear an even number of times.
Decide between using a frequency array (for a fixed character set) or a hash map (for arbitrary characters). Mention that a bitmask can be used for O(1) space if the character set is small.
Write code to count frequencies and check the number of odd counts. Analyze time complexity O(n) and space complexity O(1) or O(k) where k is the character set size.
Walk through examples like 'code' (false), 'aab' (true), and 'carrace' (true) to verify the solution and edge cases.
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.
Clarify requirements and edge cases first, then propose a digit-by-digit addition from right to left, handling decimal alignment and carry. Discuss trade-offs between string manipulation and converting to numeric types, and outline a clean implementation with complexity analysis.
Pro tip: Mention that you would avoid floating-point conversion due to precision issues, and that you can pad the shorter string with leading/trailing zeros to simplify alignment. This shows awareness of real-world constraints and clean code practices.
Ask about input constraints (e.g., leading zeros, empty strings, very large numbers) and output format (e.g., preserve trailing zeros). Confirm whether the result should be trimmed of leading zeros.
Explain why string-based digit addition is preferred over converting to floating-point or integer types, citing precision and overflow concerns. Mention that you will align decimal points and process from right to left.
Describe splitting the strings into integer and fractional parts, padding the shorter fractional part with zeros, and adding each part from right to left with carry. Then combine the results and handle any final carry.
State that time complexity is O(n) where n is the length of the longer string, and space complexity is O(n) for the result. Discuss potential optimizations like in-place manipulation or using arrays for digits.
Walk through examples like '1.23' + '4.567', '0' + '0', and cases with carry propagation (e.g., '99.99' + '0.01'). Mention how you would handle leading zeros in the result.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.