I went with recursion and backtracking, swapping characters in place.
Clarify whether the string has duplicate characters and whether permutations should be unique. Then implement a backtracking algorithm that swaps characters to generate all permutations in-place, or use recursion with a prefix. Analyze time and space complexity, and discuss handling duplicates if needed.
Pro tip: At Amazon, emphasize scalability and edge cases: mention that for strings with duplicates, you can sort and skip repeated characters to avoid redundant permutations, and discuss memory usage for large strings.
Ask if the string can have duplicate characters and if permutations should be unique. Confirm the expected output format (list of strings) and constraints (e.g., string length).
Decide between backtracking with swapping (in-place) or recursion with a prefix. For duplicates, consider sorting and skipping repeated characters.
Write clean code with a recursive helper function. Use a base case when the current index reaches the end, and swap characters to generate permutations.
State that there are n! permutations, so time complexity is O(n * n!) and space complexity is O(n) for recursion stack (excluding output).
Test with empty string, single character, and strings with duplicates. Discuss how to modify the algorithm to handle duplicates efficiently.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.