feat: add swift implementation to lcof problem: No.17 (doocs#2876)

Author: klever34

lcof/面试题17. 打印从1到最大的n位数/README.md

@@ -212,6 +212,48 @@ public class Solution {
 }
 ```
 
+#### Swift
+
+```swift
+class Solution {
+    func printNumbers(_ n: Int) -> [Int] {
+        let maxNumber = maxNumberForDigits(n)
+        return Array(1...maxNumber)
+    }
+
+    private func maxNumberForDigits(_ n: Int) -> Int {
+        var maxNumber = 1
+        for _ in 0..<n {
+            maxNumber *= 10
+        }
+        return maxNumber - 1
+    }
+
+    private var s = String()
+    private var ans = [String]()
+
+    func print(_ n: Int) -> [String] {
+        for i in 1...n {
+            dfs(0, i)
+        }
+        return ans
+    }
+
+    private func dfs(_ i: Int, _ j: Int) {
+        if i == j {
+            ans.append(s)
+            return
+        }
+        let start = i > 0 ? 0 : 1
+        for k in start..<10 {
+            s.append("\(k)")
+            dfs(i + 1, j)
+            s.removeLast()
+        }
+    }
+}
+```
+
 <!-- tabs:end -->
 
 <!-- solution:end -->

lcof/面试题17. 打印从1到最大的n位数/Solution.swift

@@ -0,0 +1,37 @@
+class Solution {
+    func printNumbers(_ n: Int) -> [Int] {
+        let maxNumber = maxNumberForDigits(n)
+        return Array(1...maxNumber)
+    }
+
+    private func maxNumberForDigits(_ n: Int) -> Int {
+        var maxNumber = 1
+        for _ in 0..<n {
+            maxNumber *= 10
+        }
+        return maxNumber - 1
+    }
+
+    private var s = String()
+    private var ans = [String]()
+
+    func print(_ n: Int) -> [String] {
+        for i in 1...n {
+            dfs(0, i)
+        }
+        return ans
+    }
+
+    private func dfs(_ i: Int, _ j: Int) {
+        if i == j {
+            ans.append(s)
+            return
+        }
+        let start = i > 0 ? 0 : 1
+        for k in start..<10 {
+            s.append("\(k)")
+            dfs(i + 1, j)
+            s.removeLast()
+        }
+    }
+}