https://leetcode.com/problems/first-unique-character-in-a-string
387. First Unique Character in a String
给一个字串s，找到第一个不重复的字符回传其索引，不存在则回传-1
Example 1:
Input: s = "leetcode"
Output: 0
Example 2:
Input: s = "loveleetcode"
Outpue: 2
Example 3:
Input: s = "aabb"
Output: -1
思路：
用for循环找出只出现一次的字符
Python3 code:

大师

大师

这不是哈希表ㄇ

那就自己建 counter = {} :(counter = defaultdict(int)for i in s:counter[i] += 1