feat: add swift implementation to lcof2 problem: No.080 (doocs#3459)

Author: klever34

lcof2/剑指 Offer II 080. 含有 k 个元素的组合/README.md

@@ -151,6 +151,35 @@ func dfs(i, n, k int, t []int, res *[][]int) {
 }
 ```
 
+#### Swift
+
+```swift
+class Solution {
+    func combine(_ n: Int, _ k: Int) -> [[Int]] {
+        var res = [[Int]]()
+        dfs(1, n, k, [], &res)
+        return res
+    }
+    
+    private func dfs(_ start: Int, _ n: Int, _ k: Int, _ current: [Int], _ res: inout [[Int]]) {
+        if current.count == k {
+            res.append(current)
+            return
+        }
+        
+        if start > n {
+            return
+        }
+        
+        for i in start...n {
+            var newCurrent = current
+            newCurrent.append(i)
+            dfs(i + 1, n, k, newCurrent, &res)
+        }
+    }
+}
+```
+
 <!-- tabs:end -->
 
 <!-- solution:end -->

lcof2/剑指 Offer II 080. 含有 k 个元素的组合/Solution.swift

@@ -0,0 +1,24 @@
+class Solution {
+    func combine(_ n: Int, _ k: Int) -> [[Int]] {
+        var res = [[Int]]()
+        dfs(1, n, k, [], &res)
+        return res
+    }
+    
+    private func dfs(_ start: Int, _ n: Int, _ k: Int, _ current: [Int], _ res: inout [[Int]]) {
+        if current.count == k {
+            res.append(current)
+            return
+        }
+        
+        if start > n {
+            return
+        }
+        
+        for i in start...n {
+            var newCurrent = current
+            newCurrent.append(i)
+            dfs(i + 1, n, k, newCurrent, &res)
+        }
+    }
+}