09_queue

java/09_queue/ArrayQueue.java

@@ -0,0 +1,46 @@
+package queue;
+
+/**
+ * Created by wangzheng on 2018/10/9.
+ */
+// 用数组实现的队列
+public class ArrayQueue {
+  // 数组：items，数组大小：n
+  private String[] items;
+  private int n = 0;
+  // head表示队头下标，tail表示队尾下标
+  private int head = 0;
+  private int tail = 0;
+
+  // 申请一个大小为capacity的数组
+  public ArrayQueue(int capacity) {
+    items = new String[capacity];
+    n = capacity;
+  }
+
+  // 入队
+  public boolean enqueue(String item) {
+    // 如果tail == n 表示队列已经满了
+    if (tail == n) return false;
+    items[tail] = item;
+    ++tail;
+    return true;
+  }
+
+  // 出队
+  public String dequeue() {
+    // 如果head == tail 表示队列为空
+    if (head == tail) return null;
+    // 为了让其他语言的同学看的更加明确，把--操作放到单独一行来写了
+    String ret = items[head];
+    ++head;
+    return ret;
+  }
+
+  public void printAll() {
+    for (int i = head; i < tail; ++i) {
+      System.out.print(items[i] + " ");
+    }
+    System.out.println();
+  }
+}

java/09_queue/CircularQueue.java

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+package queue;
+
+/**
+ * Created by wangzheng on 2018/10/9.
+ */
+public class CircularQueue {
+  // 数组：items，数组大小：n
+  private String[] items;
+  private int n = 0;
+  // head表示队头下标，tail表示队尾下标
+  private int head = 0;
+  private int tail = 0;
+
+  // 申请一个大小为capacity的数组
+  public CircularQueue(int capacity) {
+    items = new String[capacity];
+    n = capacity;
+  }
+
+  // 入队
+  public boolean enqueue(String item) {
+    // 队列满了
+    if ((tail + 1) % n == head) return false;
+    items[tail] = item;
+    tail = (tail + 1) % n;
+    return true;
+  }
+
+  // 出队
+  public String dequeue() {
+    // 如果head == tail 表示队列为空
+    if (head == tail) return null;
+    String ret = items[head];
+    head = (head + 1) % n;
+    return ret;
+  }
+
+  public void printAll() {
+    for (int i = head; i < tail; ++i) {
+      System.out.print(items[i] + " ");
+    }
+    System.out.println();
+  }
+}

java/09_queue/DynimacArrayQueue.java

@@ -0,0 +1,56 @@
+package queue;
+
+/**
+ * Created by wangzheng on 2018/10/9.
+ */
+public class DynimacArrayQueue {
+  // 数组：items，数组大小：n
+  private String[] items;
+  private int n = 0;
+  // head表示队头下标，tail表示队尾下标
+  private int head = 0;
+  private int tail = 0;
+
+  // 申请一个大小为capacity的数组
+  public DynimacArrayQueue(int capacity) {
+    items = new String[capacity];
+    n = capacity;
+  }
+
+  // 入队操作，将item放入队尾
+  public boolean enqueue(String item) {
+    // tail == n表示队列末尾没有空间了
+    if (tail == n) {
+      // tail ==n && head==0，表示整个队列都占满了
+      if (head == 0) return false;
+      // 数据搬移
+      for (int i = head; i < tail; ++i) {
+        items[i-head] = items[i];
+      }
+      // 搬移完之后重新更新head和tail
+      tail -= head;
+      head = 0;
+    }
+
+    items[tail] = item;
+    tail++;
+    return true;
+  }
+
+  // 出队
+  public String dequeue() {
+    // 如果head == tail 表示队列为空
+    if (head == tail) return null;
+    // 为了让其他语言的同学看的更加明确，把--操作放到单独一行来写了
+    String ret = items[head];
+    ++head;
+    return ret;
+  }
+
+  public void printAll() {
+    for (int i = head; i < tail; ++i) {
+      System.out.print(items[i] + " ");
+    }
+    System.out.println();
+  }
+}

java/09_queue/QueueBasedOnLinkedList.java

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+package queue;
+
+/**
+ * 基于链表实现的队列
+ *
+ * Author: Zheng
+ */
+public class QueueBasedOnLinkedList {
+
+  // 队列的队首和队尾
+  private Node head = null;
+  private Node tail = null;
+
+  // 入队
+  public void enqueue(String value) {
+    if (tail == null) {
+      Node newNode = new Node(value, null);
+      head = newNode;
+      tail = newNode;
+    } else {
+      tail.next = new Node(value, null);
+      tail = tail.next;
+    }
+  }
+
+  // 出队
+  public String dequeue() {
+    if (head == null) return null;
+
+    String value = head.data;
+    head = head.next;
+    if (head == null) {
+      tail = null;
+    }
+    return value;
+  }
+
+  public void printAll() {
+    Node p = head;
+    while (p != null) {
+      System.out.print(p.data + " ");
+      p = p.next;
+    }
+    System.out.println();
+  }
+
+  private static class Node {
+    private String data;
+    private Node next;
+
+    public Node(String data, Node next) {
+      this.data = data;
+      this.next = next;
+    }
+
+    public String getData() {
+      return data;
+    }
+  }
+
+}