feat: add swift implementation to lcof problem: No.46 (doocs#2927)

Author: klever34

lcof/面试题46. 把数字翻译成字符串/README.md

@@ -252,6 +252,38 @@ public class Solution {
 }
 ```
 
+#### Swift
+
+```swift
+class Solution {
+    private var n: Int = 0
+    private var s: [Character] = []
+    private var memo: [Int?] = []
+
+    func translateNum(_ num: Int) -> Int {
+        s = Array(String(num))
+        n = s.count
+        memo = [Int?](repeating: nil, count: n)
+        return dfs(0)
+    }
+
+    private func dfs(_ i: Int) -> Int {
+        if i >= n - 1 {
+            return 1
+        }
+        if let cachedResult = memo[i] {
+            return cachedResult
+        }
+        var ans = dfs(i + 1)
+        if s[i] == "1" || (s[i] == "2" && s[i + 1] < "6") {
+            ans += dfs(i + 2)
+        }
+        memo[i] = ans
+        return ans
+    }
+}
+```
+
 <!-- tabs:end -->
 
 <!-- solution:end -->

lcof/面试题46. 把数字翻译成字符串/Solution.swift

@@ -0,0 +1,27 @@
+class Solution {
+    private var n: Int = 0
+    private var s: [Character] = []
+    private var memo: [Int?] = []
+
+    func translateNum(_ num: Int) -> Int {
+        s = Array(String(num))
+        n = s.count
+        memo = [Int?](repeating: nil, count: n)
+        return dfs(0)
+    }
+
+    private func dfs(_ i: Int) -> Int {
+        if i >= n - 1 {
+            return 1
+        }
+        if let cachedResult = memo[i] {
+            return cachedResult
+        }
+        var ans = dfs(i + 1)
+        if s[i] == "1" || (s[i] == "2" && s[i + 1] < "6") {
+            ans += dfs(i + 2)
+        }
+        memo[i] = ans
+        return ans
+    }
+}