[Swift]LeetCode248.對稱數 III $ Strobogrammatic Number III

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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 count the total strobogrammatic numbers that exist in the range of low <= num <= high.

Example:

Input: low = "50", high = "100"
Output: 3 
Explanation: 69, 88, and 96 are three strobogrammatic numbers.

Note:
Because the range might be a large number, the lowand high numbers are represented as string.

---

strobogramatic數字是旋轉180度時看起來相同的數字（上下顛倒）。

編寫一個函數來計算在low<=num<=high範圍內存在的總strobogrammatic數。

例子：

輸入：low=「50」，high=「100」

輸出：3

說明：6九、88和96是三個strobogramatic數字。

注：

由於範圍多是一個大數字，因此低數字和高數字表示爲字符串。

---

 1 class Solution {
 2     func strobogrammaticInRange(_ low:String,_ high:String) -> Int {
 3         var res:Int = 0
 4         find(low, high, "",  &res)
 5         find(low, high, "0", &res)
 6         find(low, high, "1", &res)
 7         find(low, high, "8", &res)
 8         return res;
 9     }
10     
11     func find (_ low:String,_ high:String,_ w:String,_ res:inout Int)
12     {
13         if w.count >= low.count && w.count <= high.count
14         {
15             if (w.count == low.count && w < low) || (w.count == high.count && w > high)
16             {
17                 return 
18             }
19             if !(w.count > 1 && w[0] == "0")
20             {
21                 res += 1
22             }
23         }
24         if w.count + 2 > high.count
25         {
26             return
27         }
28         find(low, high, "0" + w + "0", &res)
29         find(low, high, "1" + w + "1", &res)
30         find(low, high, "6" + w + "9", &res)
31         find(low, high, "8" + w + "8", &res)
32         find(low, high, "9" + w + "6", &res)
33     }
34 }
35 
36 extension String {        
37     //subscript函數能夠檢索數組中的值
38     //直接按照索引方式截取指定索引的字符
39     subscript (_ i: Int) -> Character {
40         //讀取字符
41         get {return self[index(startIndex, offsetBy: i)]}
42     }
43 }