（2）Go实现顺序队列

队列是一种线性结构
只能从一端（队尾）添加元素，只能从另一端（队首）取出元素，属于先进先出的结构

// 顺序队列的实现

type queue interface{}

type sliceQueue struct {
    queues []queue
}

func NewQueue() *sliceQueue {
    return &sliceQueue{}
}

func (i *sliceQueue) Len() int {
    return len(i.queues)
}

func (i *sliceQueue) Cap() int {
    return cap(i.queues)
}

func (i *sliceQueue) Enqueue(item interface{}) {
    i.queues = append(i.queues, item)
}

func (i *sliceQueue) Dequeue() (queue, error) {
    if i.Len() == 0 {
        return nil, errors.New(
            "failed to dequeue,queue is empty ")
    }

    queue := i.queues[0]
    i.queues = i.queues[1:]
    return queue, nil
}

func (i *sliceQueue) GetFront() (queue, error) {
    if i.Len() == 0 {
        return nil, errors.New(
            "failed to getFront,queue is empty ")
    }
    return i.queues[0], nil
}

func (i *sliceQueue) IsEmpty() bool {
    return i.Len() == 0
}

// 队列测试
func main() {
    a := queue3.NewQueue()

    for i := 0; i < 5; i++ {
        a.Enqueue(strconv.Itoa(i) + "-hello toilet ")
    }

    fmt.Printf("isEmpty: %v, len=%v, cap=%v, getFront=%v\n",
        a.IsEmpty(), a.Len(), a.Cap(), fmt.Sprintln(a.GetFront()))
    fmt.Printf("isEmpty: %v, len=%v, cap=%v, dequeue=%v\n",
        a.IsEmpty(), a.Len(), a.Cap(), fmt.Sprintln(a.Dequeue()))
    fmt.Printf("isEmpty: %v, len=%v, cap=%v, dequeue=%v\n",
        a.IsEmpty(), a.Len(), a.Cap(), fmt.Sprintln(a.Dequeue()))
    fmt.Printf("isEmpty: %v, len=%v, cap=%v, dequeue=%v\n",
        a.IsEmpty(), a.Len(), a.Cap(), fmt.Sprintln(a.Dequeue()))
    fmt.Printf("isEmpty: %v, len=%v, cap=%v, dequeue=%v\n",
        a.IsEmpty(), a.Len(), a.Cap(), fmt.Sprintln(a.Dequeue()))
    fmt.Printf("isEmpty: %v, len=%v, cap=%v, dequeue=%v\n",
        a.IsEmpty(), a.Len(), a.Cap(), fmt.Sprintln(a.Dequeue()))
    fmt.Printf("isEmpty: %v, len=%v, cap=%v, dequeue=%v\n",
        a.IsEmpty(), a.Len(), a.Cap(), fmt.Sprintln(a.Dequeue()))
    fmt.Printf("isEmpty: %v, len=%v, cap=%v, getFront=%v\n",
        a.IsEmpty(), a.Len(), a.Cap(), fmt.Sprintln(a.GetFront()))
}

// 测试结果
isEmpty: false, len=5, cap=8, getFront=0-hello toilet  <nil>
isEmpty: false, len=5, cap=8, dequeue=0-hello toilet  <nil>
isEmpty: false, len=4, cap=7, dequeue=1-hello toilet  <nil>
isEmpty: false, len=3, cap=6, dequeue=2-hello toilet  <nil>
isEmpty: false, len=2, cap=5, dequeue=3-hello toilet  <nil>
isEmpty: false, len=1, cap=4, dequeue=4-hello toilet  <nil>
isEmpty: true, len=0, cap=3, dequeue=<nil> failed to dequeue,queue is empty 
isEmpty: true, len=0, cap=3, getFront=<nil> failed to getFront,queue is empty 

顺序队列的缺陷是每次取出元素，都要重新遍历一次队列，时间复杂度为O(n)，冗余操作太多

下面链接有更好的实现方法，循环队列
https://www.jianshu.com/p/8a26bedb48a1