feat: add swift implementation to lcof problem: No.44 (doocs#2925)

Author: klever34

lcof/面试题44. 数字序列中某一位的数字/README.md

@@ -166,6 +166,37 @@ public class Solution {
 }
 ```
 
+#### Swift
+
+```swift
+class Solution {
+    func findNthDigit(_ n: Int) -> Int {
+        var n = n
+        var k = 1
+        var count = 9
+
+        while k * count < n {
+            n -= k * count
+            k += 1
+            count *= 10
+        }
+
+        let num = Int(Double(10).power(Double(k - 1))) + (n - 1) / k
+        let idx = (n - 1) % k
+        let numString = String(num)
+        let char = numString[numString.index(numString.startIndex, offsetBy: idx)]
+
+        return char.wholeNumberValue!
+    }
+}
+
+extension Double {
+    func power(_ exponent: Double) -> Double {
+        return pow(self, exponent)
+    }
+}
+```
+
 <!-- tabs:end -->
 
 <!-- solution:end -->

lcof/面试题44. 数字序列中某一位的数字/Solution.swift

@@ -0,0 +1,26 @@
+class Solution {
+    func findNthDigit(_ n: Int) -> Int {
+        var n = n
+        var k = 1
+        var count = 9
+        
+        while k * count < n {
+            n -= k * count
+            k += 1
+            count *= 10
+        }
+        
+        let num = Int(Double(10).power(Double(k - 1))) + (n - 1) / k
+        let idx = (n - 1) % k
+        let numString = String(num)
+        let char = numString[numString.index(numString.startIndex, offsetBy: idx)]
+        
+        return char.wholeNumberValue!
+    }
+}
+
+extension Double {
+    func power(_ exponent: Double) -> Double {
+        return pow(self, exponent)
+    }
+}