循环队列

做的就是利用循环来解决空间浪费的问题

package main

import (
	"errors"
	"fmt"
	"strconv"
)

// 循环队列实现方法
type loopQueue struct {
	queues   []interface{}
	front    int //队首
	tail     int //队尾
	length   int //队伍长度
	capacity int //队伍容量
}

// 创建循环队列，可指定容量，默认为0
func NewLoopQueue(args ...int) *loopQueue {
	var capacity int
	if len(args) == 1 {
		capacity = args[0]
	} else if len(args) > 1 {
		panic("params invalid")
	}

	loop := &loopQueue{
		queues: make([]interface{}, 0, capacity),
	}
	//初始化队列
	for i := 0; i < capacity; i++ {
		loop.queues = append(loop.queues, "")
	}
	return loop
}

func (q *loopQueue) Len() int {
	return q.length
}

func (q *loopQueue) Cap() int {
	return q.capacity
}

func (q *loopQueue) IsEmpty() bool {
	return q.length == 0
}

func (q *loopQueue) IsFull() bool {
	return (q.length + 1) >= q.capacity
}

func (q *loopQueue) GetFront() (interface{}, error) {
	if q.Len() == 0 {
		return nil, errors.New(
			"failed to getFront,queues is empty.")
	}
	return q.queues[q.front], nil
}

// 向队尾增加元素
func (q *loopQueue) Enqueue(elem interface{}) {
	// 队列扩容
	if q.IsFull() {
		buffer := new(loopQueue)
		//初始化队列
		bufCap := 2 * q.capacity
		if bufCap == 0 {
			bufCap = 1
		}
		for i := 0; i < bufCap; i++ {
			buffer.queues = append(buffer.queues, "")
		}
		for i := 0; i < q.length; i++ {
			buffer.queues[i] = q.queues[q.front]
			q.front = (q.front + 1) % q.capacity
		}
		q.queues = buffer.queues
		q.front = 0
		q.tail = q.length
		q.capacity = bufCap
	}

	q.queues[q.tail] = elem
	q.tail = (q.tail + 1) % q.capacity
	q.length++

}
// 从循环队列中队首取出元素
func (q *loopQueue) Dequeue() (interface{}, error) {
	if q.IsEmpty() {
		return nil, errors.New("failed to dequeue,queues is empty")
	}
	// 当队列长度小于容量1/4时，队列容量缩短一半
	if q.length <= q.capacity/4 {
		buffer := new(loopQueue)
		//初始化队列
		for i := 0; i < q.capacity/2; i++ {
			buffer.queues = append(buffer.queues, "")
		}
		for i := 0; i < q.length; i++ {
			buffer.queues[i] = q.queues[q.front]
			q.front = (q.front + 1) % q.capacity
		}
		q.queues = buffer.queues
		q.front = 0
		q.tail = q.length
		q.capacity = q.capacity / 2
	}

	value := q.queues[q.front]
	q.front = (q.front + 1) % q.capacity
	q.length--
	return value, nil
}

// 测试队列
func main() {
	q := NewLoopQueue()
	for i := 0; i < 5; i++ {
		q.Enqueue(fmt.Sprintln(strconv.Itoa(i)))
	}
	fmt.Printf("isEmpty:%v, isFull:%v, len=%v, cap=%v, getFront=%v\n",
		q.IsEmpty(), q.IsFull(), q.Len(), q.Cap(), fmt.Sprintln(q.GetFront()))
	fmt.Printf("isEmpty:%v, isFull:%v, len=%v, cap=%v, dequeue=%v\n",
		q.IsEmpty(), q.IsFull(), q.Len(), q.Cap(), fmt.Sprintln(q.Dequeue()))
	fmt.Printf("isEmpty:%v, isFull:%v, len=%v, cap=%v, dequeue=%v\n",
		q.IsEmpty(), q.IsFull(), q.Len(), q.Cap(), fmt.Sprintln(q.Dequeue()))
	fmt.Printf("isEmpty:%v, isFull:%v, len=%v, cap=%v, dequeue=%v\n",
		q.IsEmpty(), q.IsFull(), q.Len(), q.Cap(), fmt.Sprintln(q.Dequeue()))
	fmt.Printf("isEmpty:%v, isFull:%v, len=%v, cap=%v, dequeue=%v\n",
		q.IsEmpty(), q.IsFull(), q.Len(), q.Cap(), fmt.Sprintln(q.Dequeue()))
	fmt.Printf("isEmpty:%v, isFull:%v, len=%v, cap=%v, dequeue=%v\n",
		q.IsEmpty(), q.IsFull(), q.Len(), q.Cap(), fmt.Sprintln(q.Dequeue()))
	fmt.Printf("isEmpty:%v, isFull:%v, len=%v, cap=%v, dequeue=%v\n",
		q.IsEmpty(), q.IsFull(), q.Len(), q.Cap(), fmt.Sprintln(q.Dequeue()))
	fmt.Printf("isEmpty:%v, isFull:%v, len=%v, cap=%v, getFront=%v\n",
		q.IsEmpty(), q.IsFull(), q.Len(), q.Cap(), fmt.Sprintln(q.GetFront()))
}