387. First Unique Character in a String 难度：easy

题目：

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.

思路：

首先这里假设只有小写字母，自然想到开一个大小为26的数组，保存每个字母出现的次数，然后在扫描一次字符串。

程序：

class Solution {
public:
    int firstUniqChar(string s) {
        int len = s.length(), i;
        map<char, int> map1;
        for(i = 0; i < len; i++){
            map1[s[i]]++;
        }
        for(i = 0; i < len; i++){
           if(map1[s[i]] == 1)
                return i;
        }
        return -1;
    
    }
};