First non-repeating character
beginner Map & Set Challenge 3 of 18
Write firstUniqueChar(str), which returns the first character in str that occurs exactly once. The starter returns the first character whatever its count, so it passes some cases by luck.
Requirements
- Return the character as a one-character string.
- Return
nullwhen there is no such character, including for an empty string. - Treat upper and lower case as different characters.
- Aim for O(n) time.
Expected output
firstUniqueChar('swiss') → 'w' firstUniqueChar('aabb') → null firstUniqueChar('') → null
Test cases (6)
- ○finds the first unique character
- ○unique character at the end
- ○returns null when every character repeats
- ○returns null for an empty string
- ○is case-sensitive
- ○handles a single character
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Results
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