leetcode Keyboard Row 键盘行

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.

在leetcode上看到的一个解法：

class Solution {
public:
    vector<string> findWords(vector<string>& words) {
        vector<string> res;
        for (auto str : words) {
            bool r1 = str.find_first_of("QWERTYUIOPqwertyuiop") == string::npos ? false : true;
            bool r2 = str.find_first_of("ASDFGHJKLasdfghjkl") == string::npos ? false : true;
            bool r3 = str.find_first_of("ZXCVBNMzxcvbnm") == string::npos ? false : true;
            if (r1 + r2 + r3 == 1)
                res.push_back(str);
        }
        return res;
    }
};

c++中的string.find()函数，查找失败时返回npos，其中npos定义为static const size_type npos = -1;