我直接写成：

var strArr = ["d", "cd", "bcd", "abcd", "abc", "ab", "a"]

sorted( strArr )

func compareTwoString(s1:String, s2:String)->Bool{return

    countElements(s1) < countElements(s2) || countElements(s1) == countElements(s2) ? (s1 < s2) : false

}

sorted(strArr, compareTwoString )

可以实现  但是 请老师帮看看