Find the first non-repeated character in a string

Question

I read of a job interview question to write some code for the following:

Write an efficient function to find the first nonrepeated character in a st

Answer 1

I think the worst case is O(n^2) but looks clear for me:

def firstNonRep(word):
    """the first non-repeating character in a string: "ABCA" -> B """
    for (i, c) in enumerate(word):
        residual = word[i+1:]
        if not c in residual:
            return c