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Queue.js
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Queue.js
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import DoublyNode from './Node/DoublyNode'
export default function Queue() {
this.front = null
this.back = null
this.enqueue = item => {
let newNode = new DoublyNode(item)
if(!this.front) {
this.front = newNode
this.back = newNode
return
}
this.back.next = newNode
newNode.prev = this.back
this.back = newNode
}
this.printForward = () => {
let vals = ''
let n = this.front
while(n) {
vals += `${n.val} -> `
n = n.next
}
return `${vals}null`
}
this.printBackward = () => {
let vals = ''
let n = this.back
while(n) {
vals = ` <- ${n.val}`.concat(vals)
n = n.prev
}
return `null${vals}`
}
this.dequeue = () => {
// remove from the front and return the removed node's val
if(!this.front) return null
let firstNode = this.front
this.front = this.front.next
// edge case: if this.front.next is null, the next line of
// code will fail because can't dereference null pointer
if(this.front) {
this.front.prev = null
} else {
this.back = null
}
firstNode.next = null
return firstNode.val
}
this.peek = () => {
if(!this.front) return null
return this.front.val
}
this.isEmpty = () => {
return !this.front
}
}