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$ curl repovive.com/roadmaps/python/tuples-sets/first-unique-implementation

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$ curl repovive.com/roadmaps/python/tuples-sets/first-unique-implementation

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First Unique - Implementation - Tuples & Sets | Python | Repovive

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First Unique - Implementation

The code

Here's the solution:

def first_unique_char(s):
    # Count occurrences
    counts = {}
    for char in s:
        counts[char] = counts.get(char, 0) + 1

    # Find first with count 1
    for char in s:
        if counts[char] == 1:
            return char

    return "None"

The first loop builds the frequency count. The second loop finds the first character with count exactly $1$ .

Time: $O(n)$ for two passes through the string. Space: $O(k)$ where $k$ is unique characters.