添加 232.用栈实现队列 Swift版本

problems/0232.用栈实现队列.md

@@ -349,6 +349,43 @@ MyQueue.prototype.empty = function() {
 };
  ```
 
+Swift：
+```swift
+class MyQueue {
+    
+    var stackIn = [Int]()
+    var stackOut = [Int]()
+    
+    init() {}
+    
+    /** Push element x to the back of queue. */
+    func push(_ x: Int) {
+        stackIn.append(x)
+    }
+    
+    /** Removes the element from in front of queue and returns that element. */
+    func pop() -> Int {
+        if stackOut.isEmpty {
+            while !stackIn.isEmpty {
+                stackOut.append(stackIn.popLast()!)
+            }
+        }
+        return stackOut.popLast() ?? -1
+    }
+    
+    /** Get the front element. */
+    func peek() -> Int {
+        let res = pop()
+        stackOut.append(res)
+        return res
+    }
+    
+    /** Returns whether the queue is empty. */
+    func empty() -> Bool {
+        return stackIn.isEmpty && stackOut.isEmpty
+    }
+}
+```
 
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