[LeetCode]First Unique Character in a String

题目描述：

LeetCode 387. First Unique Character in a String

Given a string, find the first non-repeating character in it and return it's index. If it doesn't exist, return -1.

Examples:

s = "leetcode"
return 0.

s = "loveleetcode",
return 2.

Note: You may assume the string contain only lowercase letters.

题目大意：

给定一个字符串，寻找第一个不重复字符并返回其下标。如果不存在，返回-1。

注意：你可以假设字符串不包含小写字母。

解题思路：

首先统计每个字符的出现次数，然后遍历一次原字符串。

Python代码：

class Solution(object):
    def firstUniqChar(self, s):
        """
        :type s: str
        :rtype: int
        """
        d = collections.Counter(s)
        ans = -1
        for x, c in enumerate(s):
            if d[c] == 1:
                ans = x
                break
        return ans