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.

int firstUniqChar(char* s) {
    int len  = strlen(s);
    int frequency[26]={0};
    for(int i=0;i<len;i++){
        frequency[s[i]-'a']++;
    }
    for(int i=0;i<len;i++){
        if(frequency[s[i]-'a']==1)
            return i;
    }
    return -1;

}