問題描述：Given a List of Words, return the words that can be typed using letters of alphabet on only one row's of American keyboard like the image below.

Example 1:

Input: ["Hello", "Alaska", "Dad", "Peace"]Output: ["Alaska", "Dad"]
Note:
You may use one character in the keyboard more than once.You may assume the input string will only contain letters of alphabet.分析：給出n個字符串，從而判斷每個字符串中的字符石頭來自美式鍵盤上的同一行，若來自同一行，返回該string。過程將鍵盤上的每行字符存儲到相應的vector或者數組中，然后循環Input中的每個string，并且循環string中的每個char，從而進行比較。
class Solution {public:    vector<string> findWords(vector<string>& words) {        std::unordered_set <char> row1={'q','w','e','r','t','y','u','i','o','p'};        std::unordered_set <char> row2={'a','s','d','f','g','h','j','k','l'};        std::unordered_set <char> row3={'z','x','c','v','b','n','m'};        vector<string> out;        for(auto &elem : words)        {            bool d1=true,d2=true,d3=true;            for(auto &key :elem)            {                if(d1)                {                    auto re=row1.find(tolower(key));                    if(re==row1.end())                        d1=false;                }                if(d2)                {                    auto re=row2.find(tolower(key));                    if(re==row2.end())                        d2=false;                }                if(d3)                {                    auto re=row3.find(tolower(key));                    if(re==row3.end())                        d3=false;                }                            }            if(d1||d2||d3)                out.push_back(elem);        }                return out;    }};