LeetCode/solutions/387. First Unique Character in a String.md

# [387. First Unique Character in a String](https://leetcode.com/problems/first-unique-character-in-a-string/description/)
# 思路
先遍历一遍字符串，记录每个字符出现的次数，再遍历一遍找出第一个没有重复的字符。   
由于题目说了全部字符都是小写字母，所以开辟一个大小为26的数组记录字符出现次数即可。   
时间复杂度O(n)   
# C++
```C++
class Solution {
public:
    int firstUniqChar(string s) {
        vector<int>count(26, 0);
        for(int i = 0; i < s.size(); i++) count[s[i] - 'a']++;
        for(int i = 0; i < s.size(); i++) 
            if(count[s[i] - 'a'] == 1) return i;
        return -1;
    }
};
```