添加 225. 用队列实现栈 Swift版本

problems/0225.用队列实现栈.md

@@ -598,5 +598,124 @@ MyStack.prototype.empty = function() {
 
 ```
 
+Swift
+```Swift
+// 定义一个队列数据结构
+class Queue {
+    var array: [Int]
+    init() {
+        array = [Int]()
+    }
+    
+    /** Push element x to the back of queue. */
+    func push(_ x: Int) {
+        array.append(x)
+    }
+    
+    /** Removes the element from in front of queue and returns that element. */
+    func pop() -> Int {
+        if array.isEmpty {
+            return -1
+        }
+        return array.removeFirst()
+    }
+    
+    /** Get the front element. */
+    func peek() -> Int {
+        if array.isEmpty {
+            return -1
+        }
+        return array.first!
+    }
+    
+    /** Returns whether the queue is empty. */
+    func empty() -> Bool {
+        return array.isEmpty
+    }
+    
+    func count() -> Int {
+        return array.count
+    }
+}
+
+// 使用双队列
+class MyStack {
+    var queue1: Queue
+    var queue2: Queue
+    
+    init() {
+        queue1 = Queue()
+        queue2 = Queue()
+    }
+    
+    func push(_ x: Int) {
+        queue1.push(x)
+    }
+    
+    func pop() -> Int {
+        if queue1.empty() {
+            return -1
+        }
+        while queue1.count() > 1 {
+            queue2.push(queue1.pop())
+        }
+        let res = queue1.pop()
+        while !queue2.empty() {
+            queue1.push(queue2.pop())
+        }
+        return res
+    }
+    
+    func top() -> Int {
+        if queue1.empty() {
+            return -1
+        }
+        let res = pop()
+        push(res)
+        return res
+    }
+    
+    func empty() -> Bool {
+        return queue1.empty() && queue2.empty()
+    }
+}
+
+// 使用单队列
+class MyStack {
+    var queue: Queue
+    
+    init() {
+        queue = Queue()
+    }
+    
+    func push(_ x: Int) {
+        queue.push(x)
+    }
+    
+    func pop() -> Int {
+        if queue.empty() {
+            return -1
+        }
+        for _ in 1 ..< queue.count() {
+            queue.push(queue.pop())
+        }
+        return queue.pop()
+    }
+    
+    func top() -> Int {
+        if queue.empty() {
+            return -1
+        }
+        let res = pop()
+        push(res)
+        return res
+    }
+    
+    func empty() -> Bool {
+        return queue.empty()
+    }
+}
+```
+
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