← Salesforce Interview Insights
My first instinct was to just check character frequencies and call it a day, but that's not quite right.
Use a two-pointer technique to find mismatched character pairs from both ends of the string. If there are zero mismatches, check if the string has a duplicate character to swap; if there are exactly two mismatches, verify that swapping them makes the string a palindrome; otherwise, return false.
Pro tip: Clarify edge cases upfront, such as strings of length 1 or 2, and explicitly state that swapping identical characters is allowed only if a duplicate exists. This shows attention to detail and prevents incorrect assumptions.
Confirm that 'at most once' means you can perform zero or one swap, and that swapping two identical characters is allowed only if such a pair exists. Ask about input constraints (e.g., length, character set) to guide your solution.
Initialize left and right pointers at the start and end of the string. Move them inward while characters match, and record the indices where they differ.
If there are no mismatches, check if the string contains any duplicate character (e.g., using a set or frequency count). If yes, return true; otherwise, false. If there are exactly two mismatches, check if swapping the characters at those indices makes the string a palindrome. If there are more than two mismatches, return false.
For the two-mismatch case, after swapping, ensure the entire string is a palindrome by continuing the two-pointer check or by verifying that the swapped characters match their counterparts.
State that the time complexity is O(n) and space is O(1) (or O(n) if using a set for duplicates). Mention edge cases like empty string, single character, and strings with all identical characters.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.