Leetcode500. Keyboard Row

class Solution {
public:
    
    vector<string> findWords(vector<string>& words) {
        vector<string> ret;
        int sz=words.size();
        for(int i=0;i<sz;i++){
            if(isOnlyOne(words[i]))
                ret.push_back(words[i]);
        }
        return ret;
    }
    private:
    bool isOnlyOne(const string&s){
        static const string key[]={"qwertyuiop","asdfghjkl","zxcvbnm"};
        int sz=s.size();
        int o=0;
        for(int i=0;i<sz;i++){
            for(int k=0;k<3;k++){
                if(find(key[k].begin(),key[k].end(),tolower(s[i]))!=key[k].end()){
                    if(!i) o=k;
                    else {
                        if(k!=o) return false;
                    }
                }
            }
        }
        return true;
    }
};