From 3169bc2688d702a1b8b367a6cf94db1ef88bf345 Mon Sep 17 00:00:00 2001
From: Powerstot <77142630+Powerstot@users.noreply.github.com>
Date: Tue, 18 May 2021 17:52:35 +0800
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修改0225.用队列实现栈 Java版本
---
 problems/0225.用队列实现栈.md | 90 ++++++++++++++++++++++++++++-
 1 file changed, 89 insertions(+), 1 deletion(-)

diff --git a/problems/0225.用队列实现栈.md b/problems/0225.用队列实现栈.md
index 4018364a..8dff2b86 100644
--- a/problems/0225.用队列实现栈.md
+++ b/problems/0225.用队列实现栈.md
@@ -156,6 +156,7 @@ public:
 
 Java：
 
+使用两个 Queue 实现
 ```java
 class MyStack {
 
@@ -205,7 +206,94 @@ class MyStack {
  * boolean param_4 = obj.empty();
  */
 ```
+使用两个 Deque 实现
+```java
+class MyStack {
+    // Deque 接口继承了 Queue 接口
+    // 所以 Queue 中的 add、poll、peek等效于 Deque 中的 addLast、pollFirst、peekFirst
+    Deque<Integer> que1; // 和栈中保持一样元素的队列
+    Deque<Integer> que2; // 辅助队列
+    /** Initialize your data structure here. */
+    public MyStack() {
+        que1 = new ArrayDeque<>();
+        que2 = new ArrayDeque<>();
+    }
+    
+    /** Push element x onto stack. */
+    public void push(int x) {
+        que1.addLast(x);
+    }
+    
+    /** Removes the element on top of the stack and returns that element. */
+    public int pop() {
+        int size = que1.size();
+        size--;
+        // 将 que1 导入 que2 ，但留下最后一个值
+        while (size-- > 0) {
+            que2.addLast(que1.peekFirst());
+            que1.pollFirst();
+        }
 
+        int res = que1.pollFirst();
+        // 将 que2 对象的引用赋给了 que1 ，此时 que1，que2 指向同一个队列
+        que1 = que2;
+        // 如果直接操作 que2，que1 也会受到影响，所以为 que2 分配一个新的空间
+        que2 = new ArrayDeque<>();
+        return res;
+    }
+    
+    /** Get the top element. */
+    public int top() {
+        return que1.peekLast();
+    }
+    
+    /** Returns whether the stack is empty. */
+    public boolean empty() {
+        return que1.isEmpty();
+    }
+}
+```
+优化，使用一个 Deque 实现
+```java
+class MyStack {
+    // Deque 接口继承了 Queue 接口
+    // 所以 Queue 中的 add、poll、peek等效于 Deque 中的 addLast、pollFirst、peekFirst
+    Deque<Integer> que1;
+    /** Initialize your data structure here. */
+    public MyStack() {
+        que1 = new ArrayDeque<>();
+    }
+    
+    /** Push element x onto stack. */
+    public void push(int x) {
+        que1.addLast(x);
+    }
+    
+    /** Removes the element on top of the stack and returns that element. */
+    public int pop() {
+        int size = que1.size();
+        size--;
+        // 将 que1 导入 que2 ，但留下最后一个值
+        while (size-- > 0) {
+            que1.addLast(que1.peekFirst());
+            que1.pollFirst();
+        }
+
+        int res = que1.pollFirst();
+        return res;
+    }
+    
+    /** Get the top element. */
+    public int top() {
+        return que1.peekLast();
+    }
+    
+    /** Returns whether the stack is empty. */
+    public boolean empty() {
+        return que1.isEmpty();
+    }
+}
+```
 
 Python：
 
@@ -276,4 +364,4 @@ Go：
 * 作者微信：[程序员Carl](https://mp.weixin.qq.com/s/b66DFkOp8OOxdZC_xLZxfw)
 * B站视频：[代码随想录](https://space.bilibili.com/525438321)
 * 知识星球：[代码随想录](https://mp.weixin.qq.com/s/QVF6upVMSbgvZy8lHZS3CQ)
-<div align="center"><img src=../pics/公众号.png width=450 alt=> </img></div>
\ No newline at end of file
+<div align="center"><img src=../pics/公众号.png width=450 alt=> </img></div>