387. First Unique Character in a String - LeetCode Solution

class Solution:
    def firstUniqChar(self, s: str) -> int:
        
        dic = {}
        
        for i in range(len(s)):
            if s[i] in  dic:
                dic[s[i]] = -2
            else:
                dic[s[i]] = i
        
        for i in dic:
            if dic[i] == -2:
                continue
            else:
                return dic[i]
        return -1