Phone Keypad Mapping | Dataford Interview Questions

Given known_words and a phone-keypad letter-to-digit mapping, return the words from known_words that map to a given input number (e.g. "54653346" -> ["linkedin", "jjmldfhm"]); optimize for repeated calls

Asked in the Phone screen stage. Reported follow-up: How could this be optimized for repeated calls?

Input and Output

Implement words_for_number(known_words, mapping, input_number). known_words is a list of lowercase strings, mapping maps each character to one digit string, and input_number is a digit string. Return matching words in their original order. Repeated calls with the same known_words and mapping should reuse a precomputed index.

Constraints

1 <= len(known_words) <= 10^4
1 <= len(word) <= 100 for every word
1 <= len(input_number) <= 100
Words contain only characters present in mapping
Repeated calls may use the same known_words and mapping configuration

Function Signature

def words_for_number(known_words, mapping, input_number):

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Problem