387. First Unique Character in a String

class Solution(object):
    def firstUniqChar(self, s):
        count = {}
        pos = {}
        for i, c in enumerate(s):
            if c not in count:
                count[c] = 0
                pos[c] = i
            count[c] += 1

        possible = []
        for k in count:
            if count[k] == 1:
                possible.append(pos[k])

        if len(possible) == 0:
            return -1
        return min(possible)``