def contains_repeats(str):
    """Determines if a string has repeat letters.
 
    This function is worst case O(n) because it
    must at worst check each character in the
    string. n is the length of the string.
    
    Arguments:
        str: the string to examine for
        repeat letters

    Returns:
        True if the string contains at least
        one repeat, False otherwise 
    """
    for i in range(1, len(str)):
        if str[i] == str[i-1]:
            return True

    return False