def first_uniq_char(s):
    idx_list = []
    char_set = set()
    char_dup_set = set()
    for char in s:
        if char in char_set:
            char_set.remove(char)
            char_dup_set.add(char)
        elif char not in char_dup_set:
            char_set.add(char)

    for i in range(len(s)):
        if s[i] in char_set:
            return i
    return

# print(first_uniq_char("leetcode"))