java数据结构之队列
队列概述
队列是一种特殊的线性表,它只允许在表的前端(front)进行删除操作,而在表的后端(rear)进行插入操作。进行插入操作的端称为队尾,进行删除操作的端称为队头。队列中没有元素时,称为空队列。
–队尾(rear)——允许插入的一端
–队头(front)——允许删除的一端
队列特点:先进先出(FIFO)
线性表的操作主要包括:
(1)清空队列
(2)判断是否为空
(3)元素的个数
(4)入队列
(5)出队列
(6)取对头元素
接口
对队列的抽象数据类型定义Queue接口如下:
package com.example.code;
public interface Queue {
/**
* 清空队列
*/
public void clear();
/**
* 出队列
* @return
*/
public Object deQueue();
/**
* 判断是否为空
* @return
*/
public boolean isEmpty();
/**
* 取对头元素
* @return
*/
public Object peek();
/**
* 入队列
* @param obj
*/
public void push(Object obj);
/**
* 元素的个数
* @return
*/
public int size();
}
顺序循环队列
结构模型:
存在问题
设数组长度为M,则:
–当front=0,rear=M时,再有元素入队发生溢出——真溢出
–当front!=0,rear=M时,再有元素入队发生溢出——假溢出
解决方案
–队首固定,每次出队剩余元素向下移动——浪费时间
–循环队列
»基本思想:把队列设想成环形,让sq[0]接在sq[M-1]之后,若rear+1==M,则令rear=0;
模拟ArrayQueue实现Queue
package com.example.code;
public class MyArrayQueue implements Queue {
private static int DEFAULT_SIZE = 10;
private Object array[] = null;
private int front, rear, count; //队首,队尾标注和队列的大小
public MyArrayQueue() {
array = new Object[DEFAULT_SIZE];
front = rear = count = 0;
}
@Override
public void clear() {
for(int i=0; i<DEFAULT_SIZE; i++) {
array[i] = null;
}
front = rear = count = 0;
}
@Override
public Object deQueue() {
if(0 == count) {
throw new IllegalStateException("队列已空,无数据元素可出队列!");
} else {
Object obj = array[front];
front = (front+1)%DEFAULT_SIZE;
count --;
return obj;
}
}
@Override
public boolean isEmpty() {
if((rear == front) && (0 == count))
return true;
else
return false;
}
@Override
public Object peek() {
if(0 == count) {
throw new IllegalStateException("队列已空,无数据元素可出队列!");
} else{
return array[front];
}
}
private void expand() {
Object newArray[] = new Object[2*DEFAULT_SIZE];
for(int i=0; i<count; i++) {
newArray[i] = array[(front+i)%DEFAULT_SIZE];
}
array = newArray;
front = 0;
rear = count;
DEFAULT_SIZE = 2*DEFAULT_SIZE;
}
@Override
public void push(Object obj) {
if((rear == front) && (count>0))
expand();
array[rear] = obj;
rear = (rear+1)%DEFAULT_SIZE;
count ++;
}
@Override
public int size() {
return count;
}
}
链式队列
结构模型
模拟LinkQueue实现Queue接口
package com.example.code2;
import com.example.code.Queue;
public class MyLinkQueue implements Queue {
private Node front,rear; //队头指针和队尾指针
private int size;
public MyLinkQueue() {
front = rear = new Node();
size = 0;
}
@Override
public void clear() {
front.next = null;
rear = front;
size = 0;
}
@Override
public Object deQueue() {
Node p = front.next;
front.next = p.next;
rear = p.next;
size --;
return p.data;
}
@Override
public boolean isEmpty() {
if(size == 0)
return true;
else
return false;
}
@Override
public Object peek() {
return front.next.data;
}
@Override
public void push(Object obj) {
Node p = new Node(obj);
rear.next = p;
rear = p;
size ++;
}
@Override
public int size() {
return size;
}
public String toString() {
StringBuilder sb= new StringBuilder("[");
Node p = front;
while((p=p.next) != null) {
sb.append(p.data + ", ");
}
sb.append("]");
return sb.toString();
}
}
/**
* 链队列的结点
*
*/
class Node{
Object data; //数据元素
Node next; //后驱结点
public Node() {
this(null);
}
public Node(Object data) {
this.data = data;
this.next = null;
}
}
转载:http://blog.csdn.net/luoweifu/article/details/8507835