A Simple Double Ended Queue Datastructure
Dequeue is implemented as a doubly linked circular list with a titular head
node. By "titular head node", I mean an empty node to designate the beginning
and end of the circularly linked list. I first saw this construction in the
linux kernel source and it seem simple and elegant. I added the .length
property to use it like I was using an Array.
I was using a javascript Array as a FIFO. Somewhere between 100,000 and 200,000 entries the program performance went to hell (dev host is a MBP w/8GB RAM). 15 minutes later, I implemented a simple dequeue and my FIFO scales up to millions of entries.
It is a drop-in replacement for javascript-arrays-as-fifo.
Example: Dequeue as a replacement for an Array as a FIFO
var Dequeue = require('dequeue')
//var fifo = []
var fifo = new Dequeue()
fifo.length === 0 //=> true
fifo.push(d1)
fifo.length === 1 //=> true
fifo.unshift(d2)
fifo.pop() === d1 //=> true
fifo.push(d3)
fifo.shift() === d2 //=> true
fifo.length === 1 //=> true; only d3 is in the dequeue
API
deque = new Dequeue()
deque.push(value)
Push a value on the end.
value = deque.pop()
Remove a value off the end.
deque.unshift(value)
Push a value on the beginning.
value = deque.shift()
Remove a value off the beginning.
value = deque.last()
Examine the value of the end without removing it.
value = deque.first()
Examine the value of the beginning without removing it.
deque.empty()
Remove all entries. This is NOT a test for an empty dequeue; use deque.length
for that.
Future Development
Something this simple does not really need a roadmap. However, I am thinking of adding APIs to facilitate walking the Linked List via an iterator. It will be simple and fully backward compatible.
About the Code
I was convinced by a blog posting by Issac Z. Schlueter that I don't need semicolons. So I don't use them.