feat: add swift implementation to lcof2 problem: No.081

lcof2/剑指 Offer II 081. 允许重复选择元素的组合/README.md

@@ -258,6 +258,38 @@ public class Solution
 }
 ```
 
+#### Swift
+
+```swift
+class Solution {
+    private var ans: [[Int]] = []
+    private var target: Int = 0
+    private var candidates: [Int] = []
+
+    func combinationSum(_ candidates: [Int], _ target: Int) -> [[Int]] {
+        self.ans = []
+        self.target = target
+        self.candidates = candidates
+        dfs(0, 0, [])
+        return ans
+    }
+
+    private func dfs(_ sum: Int, _ index: Int, _ current: [Int]) {
+        if sum == target {
+            ans.append(current)
+            return
+        }
+        if sum > target {
+            return
+        }
+        for i in index..<candidates.count {
+            let candidate = candidates[i]
+            dfs(sum + candidate, i, current + [candidate])
+        }
+    }
+}
+```
+
 <!-- tabs:end -->
 
 <!-- solution:end -->

lcof2/剑指 Offer II 081. 允许重复选择元素的组合/Solution.swift

@@ -0,0 +1,27 @@
+class Solution {
+    private var ans: [[Int]] = []
+    private var target: Int = 0
+    private var candidates: [Int] = []
+
+    func combinationSum(_ candidates: [Int], _ target: Int) -> [[Int]] {
+        self.ans = []
+        self.target = target
+        self.candidates = candidates
+        dfs(0, 0, [])
+        return ans
+    }
+
+    private func dfs(_ sum: Int, _ index: Int, _ current: [Int]) {
+        if sum == target {
+            ans.append(current)
+            return
+        }
+        if sum > target {
+            return
+        }
+        for i in index..<candidates.count {
+            let candidate = candidates[i]
+            dfs(sum + candidate, i, current + [candidate])
+        }
+    }
+}