✦Sure! Let’s walk through the solution step by step. First, to make sure we’re aligned on the problem: we’re given an encryption key that maps each character to a short code, and we need to implement both encrypt and decrypt, where decrypt returns every word from the supplied word list whose encryption equals the given ciphertext.

Before the code, a quick note on loading the words. The list comes from a remote file, so fetching it on every call would be wasteful. A common approach is to wrap the loader in functools.lru_cache, so the request happens once and later calls reuse the result. This matters because decrypt may be called many times in a row.

For encryption, we iterate over the plaintext and look up each character in the key. If a character is missing we return None, otherwise we concatenate the mapped values and return the resulting string. Here is one way to put it all together:

def encrypt(key, plaintext):
    pos = ""
    for ch in plaintext:
        if ch not in key:
            return None
        pos += key[ch]
    return pos

def decrypt(key, ciphertext):
    plaintexts = set()
    for word in load_word_list():
        word = word.strip()
        if encrypt(key, word) == ciphertext:
            plaintexts.add(word)
    return plaintexts

Now, for decryption, it might be tempting to invert the mapping, but that gets ambiguous because several plaintexts can produce the same ciphertext. A simpler idea is to go forward instead: take each candidate word from the cached list, strip the trailing newline, encrypt it with the key and compare the result with the ciphertext. If they match we add the word to a set, since more than one word can match and we don’t want duplicates.

In terms of complexity, encrypt is O(L) for a word of length L, and decrypt runs encrypt once per word, so it is O(W·L) overall for W words, plus O(M) extra space for the M matches we keep. The cache adds O(W) memory for the list itself, which is usually fine.

A few edge cases worth mentioning to your interviewer: an empty ciphertext, characters that are not in the key, words with trailing whitespace, and an empty word list, in which case we simply return an empty set. You may also want to point out that the loader could fail, so in production code