2022-11-29 03:19:08 +08:00
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comments: true
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---
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2022-11-22 17:47:26 +08:00
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# 双向队列
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对于队列,我们只能在头部删除或在尾部添加元素,而「双向队列 Deque」更加灵活,在其头部和尾部都能执行元素添加或删除操作。
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![deque_operations](deque.assets/deque_operations.png)
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2022-11-23 15:50:59 +08:00
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<p align="center"> Fig. 双向队列的操作 </p>
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2022-11-22 17:47:26 +08:00
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## 双向队列常用操作
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2023-01-07 20:34:32 +08:00
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双向队列的常用操作见下表(方法命名以 Java 为例)。
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2022-11-22 17:47:26 +08:00
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2022-11-23 15:50:59 +08:00
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<p align="center"> Table. 双向队列的常用操作 </p>
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2022-11-22 17:47:26 +08:00
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<div class="center-table" markdown>
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2023-01-09 02:17:40 +08:00
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| 方法 | 描述 | 时间复杂度 |
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| ------------ | ---------------- | ---------- |
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| offerFirst() | 将元素添加至队首 | $O(1)$ |
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| offerLast() | 将元素添加至队尾 | $O(1)$ |
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| pollFirst() | 删除队首元素 | $O(1)$ |
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| pollLast() | 删除队尾元素 | $O(1)$ |
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| peekFirst() | 访问队首元素 | $O(1)$ |
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| peekLast() | 访问队尾元素 | $O(1)$ |
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| size() | 获取队列的长度 | $O(1)$ |
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| isEmpty() | 判断队列是否为空 | $O(1)$ |
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2022-11-22 17:47:26 +08:00
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</div>
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相同地,我们可以直接使用编程语言实现好的双向队列类。
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=== "Java"
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```java title="deque.java"
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/* 初始化双向队列 */
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Deque<Integer> deque = new LinkedList<>();
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2022-11-22 17:47:26 +08:00
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/* 元素入队 */
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deque.offerLast(2); // 添加至队尾
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deque.offerLast(5);
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deque.offerLast(4);
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deque.offerFirst(3); // 添加至队首
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deque.offerFirst(1);
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2022-12-03 20:25:24 +08:00
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/* 访问元素 */
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int peekFirst = deque.peekFirst(); // 队首元素
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int peekLast = deque.peekLast(); // 队尾元素
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/* 元素出队 */
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int pollFirst = deque.pollFirst(); // 队首元素出队
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int pollLast = deque.pollLast(); // 队尾元素出队
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2023-01-07 20:34:32 +08:00
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2022-11-30 02:27:26 +08:00
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/* 获取双向队列的长度 */
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int size = deque.size();
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/* 判断双向队列是否为空 */
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boolean isEmpty = deque.isEmpty();
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```
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=== "C++"
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```cpp title="deque.cpp"
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/* 初始化双向队列 */
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deque<int> deque;
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/* 元素入队 */
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deque.push_back(2); // 添加至队尾
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deque.push_back(5);
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deque.push_back(4);
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deque.push_front(3); // 添加至队首
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deque.push_front(1);
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/* 访问元素 */
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int front = deque.front(); // 队首元素
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int back = deque.back(); // 队尾元素
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/* 元素出队 */
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deque.pop_front(); // 队首元素出队
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deque.pop_back(); // 队尾元素出队
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/* 获取双向队列的长度 */
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int size = deque.size();
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/* 判断双向队列是否为空 */
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bool empty = deque.empty();
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2022-11-22 17:47:26 +08:00
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```
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=== "Python"
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```python title="deque.py"
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2022-12-02 00:09:34 +08:00
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""" 初始化双向队列 """
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duque = deque()
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2022-12-02 00:09:34 +08:00
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""" 元素入队 """
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duque.append(2) # 添加至队尾
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duque.append(5)
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duque.append(4)
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duque.appendleft(3) # 添加至队首
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duque.appendleft(1)
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""" 访问元素 """
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front = duque[0] # 队首元素
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rear = duque[-1] # 队尾元素
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2022-12-02 00:09:34 +08:00
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""" 元素出队 """
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pop_front = duque.popleft() # 队首元素出队
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pop_rear = duque.pop() # 队尾元素出队
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2022-12-02 00:09:34 +08:00
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""" 获取双向队列的长度 """
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size = len(duque)
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2022-12-02 00:09:34 +08:00
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""" 判断双向队列是否为空 """
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is_empty = len(duque) == 0
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2022-11-22 17:47:26 +08:00
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```
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2022-12-03 01:31:29 +08:00
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=== "Go"
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2022-12-15 23:30:53 +08:00
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```go title="deque_test.go"
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/* 初始化双向队列 */
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// 在 Go 中,将 list 作为双向队列使用
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deque := list.New()
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/* 元素入队 */
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deque.PushBack(2) // 添加至队尾
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deque.PushBack(5)
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deque.PushBack(4)
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deque.PushFront(3) // 添加至队首
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deque.PushFront(1)
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/* 访问元素 */
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front := deque.Front() // 队首元素
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rear := deque.Back() // 队尾元素
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/* 元素出队 */
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deque.Remove(front) // 队首元素出队
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deque.Remove(rear) // 队尾元素出队
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2022-12-03 20:25:24 +08:00
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/* 获取双向队列的长度 */
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size := deque.Len()
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/* 判断双向队列是否为空 */
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isEmpty := deque.Len() == 0
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2022-12-03 01:31:29 +08:00
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```
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=== "JavaScript"
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```js title="deque.js"
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2022-12-03 01:31:29 +08:00
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```
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=== "TypeScript"
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```typescript title="deque.ts"
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2022-12-03 01:31:29 +08:00
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```
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=== "C"
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```c title="deque.c"
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2022-12-03 01:31:29 +08:00
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```
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=== "C#"
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```csharp title="deque.cs"
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/* 初始化双向队列 */
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// 在 C# 中,将链表 LinkedList 看作双向队列来使用
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LinkedList<int> deque = new LinkedList<int>();
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/* 元素入队 */
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deque.AddLast(2); // 添加至队尾
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deque.AddLast(5);
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deque.AddLast(4);
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deque.AddFirst(3); // 添加至队首
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deque.AddFirst(1);
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/* 访问元素 */
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int peekFirst = deque.First.Value; // 队首元素
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int peekLast = deque.Last.Value; // 队尾元素
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/* 元素出队 */
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deque.RemoveFirst(); // 队首元素出队
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deque.RemoveLast(); // 队尾元素出队
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2023-01-07 20:34:32 +08:00
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2022-12-30 14:28:39 +08:00
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/* 获取双向队列的长度 */
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int size = deque.Count;
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2023-01-07 20:34:32 +08:00
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2022-12-30 14:28:39 +08:00
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/* 判断双向队列是否为空 */
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bool isEmpty = deque.Count == 0;
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2022-12-03 01:31:29 +08:00
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```
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2023-01-08 19:41:05 +08:00
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=== "Swift"
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```swift title="deque.swift"
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2023-01-14 01:06:00 +08:00
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/* 初始化双向队列 */
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// Swift 没有内置的双向队列类,可以把 Array 当作双向队列来使用
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var deque: [Int] = []
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/* 元素入队 */
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deque.append(2) // 添加至队尾
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deque.append(5)
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deque.append(4)
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deque.insert(3, at: 0) // 添加至队首
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deque.insert(1, at: 0)
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/* 访问元素 */
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let peekFirst = deque.first! // 队首元素
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let peekLast = deque.last! // 队尾元素
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/* 元素出队 */
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let pollFirst = deque.removeFirst() // 队首元素出队
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let pollLast = deque.removeLast() // 队尾元素出队
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/* 获取双向队列的长度 */
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let size = deque.count
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/* 判断双向队列是否为空 */
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let isEmpty = deque.isEmpty
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2023-01-08 19:41:05 +08:00
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```
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