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.

方法：哈希

class Solution {
public:
    int firstUniqChar(string s) {
        unordered_map<char,int> hash;
        for(int i = 0 ; i < s.size(); ++i)
            ++hash[s[i]];
        for(int i = 0 ; i < s.size(); ++i){
            if(hash[s[i]]==1)
                return i;
        }
        return -1;
    }
};