Merge pull request #914 from qxuewei/master

添加 232.用栈实现队列 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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 <div align="center"><img src=https://code-thinking.cdn.bcebos.com/pics/01二维码一.jpg width=500> </img></div>

problems/0232.用栈实现队列.md

@@ -349,6 +349,44 @@ 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
+    }
+}
+```
+
 C:
 ```C
 /*
@@ -426,6 +464,5 @@ void myQueueFree(MyQueue* obj) {
 }
 ```
 
-
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 <div align="center"><img src=https://code-thinking.cdn.bcebos.com/pics/01二维码一.jpg width=500> </img></div>