leetcode——387. 字符串中的第一个唯一字符

class Solution(object):
    def firstUniqChar(self, s):
        """
        :type s: str
        :rtype: int
        """
        k=[]
        i=0
        while i<len(s):
            if s[i] in k:
                i+=1
            elif s.count(s[i])==1:
                return i
            else:
                k.append(s[i])
                i+=1
        return -1