Level 1Exercise #22

First unique character

Return the first character seen exactly once, or None when all repeat.

Sample Test Cases

Example #1

Input:first_unique("swiss")

Output:"w"

Reference Solution

Reveal Reference Solution

def first_unique(text: str) -> str | None:
    counts = {}
    for ch in text:
        counts[ch] = counts.get(ch, 0) + 1
    for ch in text:
        if counts[ch] == 1:
            return ch
    return None

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First unique character

Sample Test Cases

Further Reading

Reference Solution