First Unique Character In A String.cpp

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