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The problem looks clean on the surface until you realize the decoder has to figure out where the dictionary ends and the index list begins just from the compressed string.
Start by clarifying the exact format of the compressed string and the constraints (e.g., delimiter choices, handling of special characters). Then design a self-contained format that embeds the dictionary and the index sequence, ensuring the decoder can parse it unambiguously. Walk through an example to validate the design and discuss trade-offs like delimiter escaping and compression ratio.
Pro tip: Choose delimiters that cannot appear in the input (e.g., '|' and ';') and explicitly state that assumption; this avoids complex escaping and keeps the solution clean. Also, mention that the decoder must parse the dictionary before the indices, so the format should place the dictionary first.
Ask about input format, allowed characters, and whether the compressed string must be human-readable. Confirm that the decoder receives only the compressed string.
Decide on a structure: dictionary entries separated by a delimiter, then a separator, then indices separated by another delimiter. Ensure the format is unambiguous and self-describing.
Split the input by commas, build a dictionary mapping unique words to indices (order of first appearance), and construct the compressed string by joining dictionary entries and indices with chosen delimiters.
Parse the compressed string by splitting on the main separator to separate dictionary from indices, then split each part by their respective delimiters. Reconstruct the original string by replacing each index with the corresponding dictionary word.
Test with edge cases (empty input, repeated words, special characters). Discuss trade-offs: delimiter choice, escaping, compression effectiveness, and alternative formats like JSON.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.