leetcode First Unique Character in a String

class Solution {
public:
    int firstUniqChar(string s) {
       map<char,int> chars;
        for(int i=0; i< s.size(); i++)
        {
            int temp = chars[s[i]];
            if(temp !=0)
            {
                chars[s[i]]=2;
            }
            else
            {
                chars[s[i]]=1;
            }
        }
        
        for(int i=0; i< s.size(); i++)
        {
            int temp = chars[s[i]];
            if(temp ==1)
            {
                return i;
            }
            
        }
        
        
        return -1;

    }
};