first-non-repeating.py

def non_repeating(data):
    count = {}

    # First pass: Count occurrences
    for char in data:
        count[char] = count.get(char, 0) + 1

    # Second pass: Find the first non-repeating character
    for char in data:
        if count[char] == 1:
            return char

    return None


if __name__ == "__main__":
    print(non_repeating("abcda"))
    print(non_repeating("aabcd"))
    print(non_repeating("hello"))

# abcda -> b
# aabcd -> b
# hello -> h