79 lines
2.2 KiB
Markdown
79 lines
2.2 KiB
Markdown
# 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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<p align="center"> Fig. 双向队列的操作 </p>
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## 双向队列常用操作
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双向队列的常用操作见下表，方法名需根据编程语言设定来具体确定。
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<p align="center"> Table. 双向队列的常用操作 </p>
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<div class="center-table" markdown>
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| 方法 | 描述 |
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| ------------ | ---------------- |
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| offerFirst() | 将元素添加至队首 |
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| offerLast() | 将元素添加至队尾 |
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| pollFirst() | 删除队首元素 |
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| pollLast() | 删除队尾元素 |
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| peekFirst() | 访问队首元素 |
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| peekLast() | 访问队尾元素 |
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| size() | 获取队列的长度 |
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| isEmpty() | 判断队列是否为空 |
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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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/* 元素入队 */
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deque.offerLast(2);
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deque.offerLast(5);
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deque.offerLast(4);
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deque.offerFirst(3);
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deque.offerFirst(1);
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System.out.println("队列 deque = " + deque);
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/* 访问队首元素 */
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int peekFirst = deque.peekFirst();
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System.out.println("队首元素 peekFirst = " + peekFirst);
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int peekLast = deque.peekLast();
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System.out.println("队尾元素 peekLast = " + peekLast);
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/* 元素出队 */
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int pollFirst = deque.pollFirst();
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System.out.println("队首出队元素 pollFirst = " + pollFirst +
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"，队首出队后 deque = " + deque);
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int pollLast = deque.pollLast();
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System.out.println("队尾出队元素 pollLast = " + pollLast +
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"，队尾出队后 deque = " + deque);
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/* 获取队列的长度 */
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int size = deque.size();
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System.out.println("队列长度 size = " + size);
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/* 判断队列是否为空 */
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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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```
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=== "Python"
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```python title="deque.py"
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```
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