题目描述：

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.

代码实现：

class Solution {
public:
    int firstUniqChar(string s) {
        int arr[26];
        for(int i=0;i<26;++i){
            arr[i]=0;
        }
        for(int i=0;i<s.size();++i){
            ++arr[s[i]-'a'];
        }
        for(int i=0;i<s.size();++i){
            if(arr[s[i]-'a']==1){
                return i;
            }
        }
        return -1;
    }
};