389. Find the Difference

static int wing=[]()
{
    std::ios::sync_with_stdio(false);
    cin.tie(NULL);
    return 0;
}();

class Solution 
{
public:
    char findTheDifference(string s, string t) 
    {
        vector<int> vi(128,0);
        for(char c:s)
            vi[c]++;
        for(char c:t)
            if(--vi[c]<0)
                return c;
    }
};

map或者vector