feat: add swift implementation to lcof problem: No.09 (#2855)

Author: klever34

lcof/面试题09. 用两个栈实现队列/README.md

@@ -336,6 +336,38 @@ public class CQueue {
  */
 ```
 
+#### Swift
+
+```swift
+class CQueue {
+    private var stk1: [Int] = []
+    private var stk2: [Int] = []
+
+    init() {
+    }
+
+    func appendTail(_ value: Int) {
+        stk1.append(value)
+    }
+
+    func deleteHead() -> Int {
+        if stk2.isEmpty {
+            while !stk1.isEmpty {
+                stk2.append(stk1.removeLast())
+            }
+        }
+        return stk2.isEmpty ? -1 : stk2.removeLast()
+    }
+}
+
+/**
+ * Your CQueue object will be instantiated and called as such:
+ * let obj = CQueue();
+ * obj.appendTail(value);
+ * let param_2 = obj.DeleteHead();
+ */
+```
+
 <!-- tabs:end -->
 
 <!-- solution:end -->

lcof/面试题09. 用两个栈实现队列/Solution.swift

@@ -0,0 +1,20 @@
+class CQueue {
+    private var stk1: [Int] = []
+    private var stk2: [Int] = []
+
+    init() {
+    }
+
+    func appendTail(_ value: Int) {
+        stk1.append(value)
+    }
+
+    func deleteHead() -> Int {
+        if stk2.isEmpty {
+            while !stk1.isEmpty {
+                stk2.append(stk1.removeLast())
+            }
+        }
+        return stk2.isEmpty ? -1 : stk2.removeLast()
+    }
+}