21 August 2026

First Unique Word

Hard Strings Dictionaries

Find the first word in a sentence that appears only once.

Given a sentence, return the first word that appears exactly once. Ignore letter case and punctuation when comparing words. A word is a consecutive run of English letters. Return the word in lowercase, or return None if every word appears more than once or the sentence contains no words.

Constraints

0 <= len(sentence) <= 1000
sentence contains English letters, whitespace, and punctuation
Compare words without letter case or punctuation
Return the result in lowercase

Function signature

def first_unique_word(sentence):

First Unique Word

Constraints

Function signature

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