[Swift]LeetCode246.对称数 $ Strobogrammatic Number

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

Write a function to determine if a number is strobogrammatic. The number is represented as a string.

Example 1:

Input:  "69"
Output: true

Example 2:

Input:  "88"
Output: true

Example 3:

Input:  "962"
Output: false

---

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

写一个函数来肯定一个数字是不是频闪的。数字用字符串表示。

例1：

输入：“69”

输出：true

例2：

输入：“88”

输出：真

例3：

输入：“962”

输出：false

---

 1 class Solution {
 2     func isStrobogrammatic(_ num:String) -> Bool {
 3         var m:[Character:Character] = ["0":"0","1":"1","8":"8","6":"9","9":"6"]
 4         let len = num.count
 5         for i in 0...len/2
 6         {
 7             if m[num[i]] != num[len - i - 1]
 8             {
 9                 return false
10             }
11         }
12         return true
13     }
14 }
15 
16 extension String {        
17     //subscript函数能够检索数组中的值
18     //直接按照索引方式截取指定索引的字符
19     subscript (_ i: Int) -> Character {
20         //读取字符
21         get {return self[index(startIndex, offsetBy: i)]}
22     }
23 }