Pretty clean once I understood the structure.
Clarify the exact separators (e.g., single space between Morse characters, triple space between words) and edge cases. Then implement a solution that splits the input by word separator, then by character separator, and maps each Morse code to its letter using a hash map. Discuss time and space complexity and test with examples.
Pro tip: Mention that you would validate the input and handle invalid Morse codes gracefully, and that you can optimize by using a trie if the mapping is large or if decoding streaming input.
Ask about the exact separators (e.g., single space vs. triple space), whether the input is guaranteed valid, and if there are any constraints on the Morse code mapping. Confirm the expected output format.
Use a hash map (dictionary) to store the Morse-to-letter mapping for O(1) lookups. Consider if a trie is more appropriate for prefix-based decoding or streaming scenarios.
Split the input string by the word separator (e.g., triple space) to get words. For each word, split by the character separator (e.g., single space) to get Morse codes, then map each code to its letter and concatenate.
Write clean code with clear variable names. Test with simple cases (single letter, single word, multiple words) and edge cases (empty string, invalid codes, extra spaces).
State time complexity O(n) where n is the length of the input string, and space complexity O(m) for the mapping and output. Discuss potential optimizations like using a trie for large mappings or streaming input.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.
Treat the problem as a recursive backtracking search over the concatenated Morse string, where at each position you try every possible Morse code (1-4 symbols) that matches a prefix and recursively decode the remainder. Accumulate all valid decodings, pruning branches that cannot lead to a complete decode. Discuss complexity and potential optimizations like memoization or dynamic programming to avoid redundant work.
Pro tip: Mention that without separators the number of decodings can be exponential, so you should discuss pruning and memoization early to show you think about scalability, not just correctness.
Confirm that the input is a single string of dots and dashes representing multiple words with no separators, and that you need to output all possible sentences (sequences of words) that can be formed using the Morse mapping. Ask about expected output size and whether duplicates are possible.
Define a recursive function that takes the remaining Morse string and returns all valid decodings. At each step, try every Morse code of length 1 to 4 that matches a prefix; if it maps to a letter, recurse on the rest and prepend the letter to each result.
Since there are no character separators inside each word, but words are separated by spaces in the original Morse (or you need to infer word breaks), decide how to insert spaces. Typically, you can treat the entire string as one word and then split into words by trying all possible space insertions, or assume the input already has spaces between words and only decode within each word.
Use a hash map to cache results for each suffix of the Morse string to avoid recomputing overlapping subproblems. This reduces time complexity from exponential to polynomial in the length of the string, though the output size can still be exponential.
Discuss the time and space complexity: worst-case O(4^n) without memoization, and with memoization O(n * L) where L is the number of valid decodings. Mention that the output itself can be exponential, so any algorithm must at least spend time proportional to the output size.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.