[Swift]LeetCode248.对称数 III $ Strobogrammatic Number III

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➤微信公众号：山青咏芝（shanqingyongzhi）

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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, thelowandhighnumbers are represented as string.

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

编写一个函数来计算在low<=num<=high范围内存在的总strobogrammatic数。

例子：

输入：low=“50”，high=“100”

输出：3

说明：69、88和96是三个strobogramatic数字。

注：

因为范围可能是一个大数字，所以低数字和高数字表示为字符串。

1 class Solution { 2func 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}1011func find (_ low:String,_ high:String,_ w:String,_ res:inout Int)12{13 if w.count >= low.count && w.count <= high.count14 {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 += 122 }23 }24 if w.count + 2 > high.count25 {26 return27 }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函数可以检索数组中的值38//直接按照索引方式截取指定索引的字符39subscript (_ i: Int) -> Character {40 //读取字符41 get {return self[index(startIndex, offsetBy: i)]}42}43 }

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