[Swift]LeetCode247.对称数 II $ Strobogrammatic Number II

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A strobogrammatic number is a number that looks the same when rotated 180 degrees (looked at upside down).

Find all strobogrammatic numbers that are of length = n.

For example,
Given n = 2, return ["11","69","88","96"].

Hint:

Try to use recursion and notice that it should recurse with n - 2 instead of n - 1.

strobogramatic数字是旋转180度时看起来相同的数字（上下颠倒）。

找到所有长度为n的频闪图。

例如，

给定n=2，返回 [“11”，“69”，“88”，“96”]。

提示：

尝试使用递归，注意它应该使用n-2而不是n-1进行递归。

 1 class Solution {
 2     func shortest(_ n:Int) -> [String] {
 3         var one:[String] = ["0","1","8"]
 4         var two:[String] = [""]
 5         var res:[String] = two
 6         if n % 2 == 1
 7         {
 8             res = one
 9         }
10         for i in stride(from: (n % 2) + 2,through: n,by: 2)
11         {
12             var t:[String] = [String]()
13             for a in res
14             {
15                 if i != n
16                 {
17                     t.append("0" + a + "0")
18                 }
19                 t.append("1" + a + "1")
20                 t.append("6" + a + "9")
21                 t.append("8" + a + "8")
22                 t.append("9" + a + "6")
23             }
24             res = t
25         }
26         return res
27     }
28 }