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;    }};