How to implement a simple queue properly?

Posted by Stephen Hsu on Stack Overflow See other posts from Stack Overflow or by Stephen Hsu
Published on 2010-06-15T03:21:32Z Indexed on 2010/06/15 4:02 UTC
Read the original article Hit count: 262

Filed under:
|

The current Go library doesn't provide the queue container. To implement a simple queue, I use circle array as the underlying data structure. It follows algorithms mentioned in TAOCP:

Insert Y into queue X: X[R]<-Y; R<-(R+1)%M; if R=F then OVERFLOW.
Delete Y from queue X: if F=R then UNDERFLOW; Y<-X[F]; F<-(F+1) % M.
F: Front, R: Rear, M: Array length.

Following is the code:

package main

import (
    "fmt"
)

type Queue struct {
    len        int 
    head, tail int 
    q          []int
}

func New(n int) *Queue {
    return &Queue{n, 0, 0, make([]int, n)} 
}

func (p *Queue) Enqueue(x int) bool {
    p.q[p.tail] = x 
    p.tail = (p.tail + 1) % p.len
    return p.head != p.tail
}

func (p *Queue) Dequeue() (int, bool) {
    if p.head == p.tail {
        return 0, false
    }   
    x := p.q[p.head]
    p.head = (p.head + 1) % p.len
    return x, true
}

func main() {
    q := New(10)
    for i := 1; i < 13; i++ {
        fmt.Println(i, q.Enqueue(i))
    }   
    fmt.Println()
    for i := 1; i < 13; i++ {
        fmt.Println(q.Dequeue())
    }   
}

But the output is obviously wrong:

1 true 2 true 3 true 4 true 5 true 6 true 7 true 8 true 9 true 10 false 11 true 12 true

11 true 12 true 0 false 0 false 0 false 0 false 0 false 0 false 0 false 0 false 0 false 0 false

I think I need one more field to make the code work properly. What do you suggest?

© Stack Overflow or respective owner

Related posts about data-structures

Related posts about go

  • Go import error while trying to import web.go package after using goinstall

    as seen on Stack Overflow - Search for 'Stack Overflow'
    With halfdans advice, I was successfully able to use goinstall github.com/hoisie/web.go without any errors after installing git first. However, now when I try to compile the sample code given, go is not finding the web package. I get the error, main.go:4: can't find import: web On this code package… >>> More

  • Go Big or Go Home

    as seen on Oracle Blogs - Search for 'Oracle Blogs'
    The Oracle Develop conference (#oracledevelop10), being co-located for the first time ever with JavaOne in San Francisco, is guaranteed to be the ultimate rush for developers this year. Where else can you go to learn about, interact with, and meet fellow devotees of the entire Oracle Development… >>> More

  • Go Big or Go Home

    as seen on Oracle Blogs - Search for 'Oracle Blogs'
    For those who don’t know, Oracle sponsors a group called “OWL” – Oracle Women’s Leadership - and the purpose of the group is to create local and global opportunities that support, educate and empower current and future women leaders at Oracle. This week, I had the opportunity to attend the Denver… >>> More

  • Go Big or Go Special

    as seen on SQL Team - Search for 'SQL Team'
    Watching Shark Tank tonight and the first presentation was by Mango Mango Preserves and it highlighted an interesting contrast in business trends today and how to capitalize on opportunities.  <Spoiler Alert> Even though every one of the sharks was raving about the product samples they tried… >>> More

  • juju bootstrap fails with a local environment, why?

    as seen on Ask Ubuntu - Search for 'Ask Ubuntu'
    Each time I try to bootstrap juju using a local enviroment it fails starting the juju-db-braiam-local script as follows: $ sudo juju --debug --verbose bootstrap 2013-10-20 02:28:53 INFO juju.provider.local environprovider.go:32 opening environment "local" 2013-10-20 02:28:53 DEBUG juju.provider.local… >>> More