Start by clarifying the requirements: null input should return false, empty string is a valid palindrome. Then implement a two-pointer approach comparing characters from both ends, ignoring case and non-alphanumeric characters if specified. Discuss time and space complexity, and consider edge cases like single character and strings with only non-alphanumeric characters.
Pro tip: Demonstrate awareness of Unicode and locale-specific characters, and mention that in production code you might normalize the string first. Also, proactively discuss the trade-off between the two-pointer approach and reversing the string, highlighting the O(1) space advantage of two-pointer.
Confirm handling of null (return false), empty string (return true), and whether to ignore case and non-alphanumeric characters. Ask about input constraints and expected character set.
Select the two-pointer technique for O(n) time and O(1) space, or string reversal for simplicity. Explain why two-pointer is more efficient in terms of space.
Write clean code: handle null and empty string first, then use two pointers moving inward, comparing characters (optionally normalizing case and skipping non-alphanumeric).
Walk through examples: null, empty string, single character, 'racecar', 'A man, a plan, a canal: Panama', and strings with mixed case or punctuation.
State time complexity O(n) and space complexity O(1) for two-pointer. Mention potential optimizations like early exit on mismatch and handling Unicode normalization.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.
The linear scan is easy: just walk through and find where the gap is.
Start by explaining the O(n) solution: compute the expected sum of the consecutive sequence and subtract the actual sum to find the missing number. Then, for O(log n), use binary search to find the first index where the value deviates from the expected value (index + offset), leveraging the sorted property.
Pro tip: Clarify that the sequence is consecutive and sorted, so the difference between the value and its index is constant until the missing number, then increases by 1. This insight is key to the binary search solution.
Restate the problem: given a sorted array of distinct integers forming a consecutive sequence with one missing number, find the missing number. Note that the sequence may not start at 0, so determine the starting value.
Explain that you can compute the expected sum of the full sequence using the arithmetic series formula, then subtract the sum of the given array. The difference is the missing number. This takes O(n) time and O(1) space.
Observe that in the complete sequence, the difference between each element and its index is constant (equal to the starting value). With one missing number, this difference remains constant until the missing number, then increases by 1 for all subsequent elements.
Use binary search to find the first index where the difference changes. Compare the difference at the middle index with the expected difference. If it's the same, the missing number is to the right; otherwise, it's to the left. Return the missing number as the value at the found index minus 1 (or based on the pattern).
State that the binary search solution runs in O(log n) time and O(1) space. Discuss edge cases: missing number at the beginning or end, array of size 1, and ensure the algorithm handles them correctly.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.