# Keyboard Row

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:**

1. You may use one character in the keyboard more than once.
2. You may assume the input string will only contain letters of alphabet.

## 解题思路：

**集合运算**

判断输入单词的字母集合是否为键盘某一行字母集合的子集

use`set`to check the word.First make every line a set of letter.Then I check every word if this word set is the subset if any line set.

```
class Solution(object):
    def findWords(self, words):
        """
        :type words: List[str]
        :rtype: List[str]
        """
        line1, line2, line3 = set('qwertyuiop'), set('asdfghjkl'), set('zxcvbnm')
        result = []
        for word in words:
            w = set(word.lower())
            if w.issubset(line1) or w.issubset(line2) or w.issubset(line3):
                result.append(word)
        return result
```

set 的issubset()

s.issubset(t) 与 s <= t 相等：test whether every element in s is in t。
