':type words: List[str]
:rtype: List[str]'

def findWords(self, words):

    rows = [set(['q', 'w', 'e', 'r', 't', 'y', 'u', 'i', 'o', 'p']), set(['a', 's', 'd', 'f', 'g', 'h', 'j', 'k', 'l']), set(['z', 'x', 'c', 'v', 'b', 'n', 'm'])]
    result = []
    for word in words:
        k = 0
        for i in xrange(len(rows)):
            if (word[0].lower() in rows[i]):
                k = i
                break
        for c in word:
            if (c.lower() not in rows[k]):
                break
        else:
            result.append(word)
    return result
