LeetCode : First Unique Character in a String

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.

class Solution {
public:
    int firstUniqChar(string s) {
        int len = s.length();
        int count[256] = {0};
        for(int i=0;i<len;++i)
        {
            count[s[i]]++;
        }
        for(int i=0;i<s.length();++i)
        {
            if(count[s[i]]==1)
               return i;
        }
        return -1;
    }
};