LeetCode 387. 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) {
        map<char, int> checked;
        for(int i=0; i<s.size(); i++)
            checked[s[i]]++;
        int index=0;
        for(; index<s.size(); index++)
            if(checked[s[index]]==1)
               break;
        return index==s.size()?-1:index;
    }
};