The core idea clicks pretty fast: count frequencies in the target, then walk through the ordering string and append each character the right number of times, then tack on whatever's left.
Clarify the problem constraints and edge cases, then propose an efficient solution using a hash map to store the custom order and a stable sort or counting sort to rearrange the target string. Analyze time and space complexity, and discuss potential optimizations or alternative approaches.
Pro tip: Mention that characters not in the custom order can be placed at the end or beginning, but be explicit about your choice and ensure it doesn't affect the relative order of the ordered characters. Also, consider using a stable sort to maintain the original order of characters with the same custom order index.
Ask about the character set (ASCII/Unicode), whether the custom order string contains duplicates, and how to handle characters not in the order. Confirm if the output should be stable for characters with the same order index.
Use a hash map to map each character in the custom order to its index. For rearranging, consider counting sort (if character set is small) or a stable sort with a custom comparator.
Iterate through the custom order, and for each character, append all its occurrences from the target string to the result. Then append any remaining characters not in the custom order. Alternatively, sort the target string using the custom order as the key.
Discuss time and space complexity. For counting sort: O(n + k) time and O(k) space, where k is the size of the custom order. For sorting: O(n log n) time. Mention trade-offs.
Walk through a few test cases, including empty strings, characters not in the order, and duplicates. Verify correctness and edge cases.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.