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3-dequeue.js
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65 lines (56 loc) · 1.27 KB
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'use strict';
class Dequeue {
constructor() {
this.first = null;
this.last = null;
}
push(item) {
const last = this.last;
const element = { prev: last, next: null, item };
if (last) last.next = element;
else this.first = element;
this.last = element;
}
pop() {
const element = this.last;
if (!element) return null;
if (this.first === element) {
this.first = null;
this.last = null;
} else {
this.last = element.prev;
this.last.next = null;
}
return element.item;
}
unshift(item) {
const first = this.first;
const element = { prev: null, next: first, item };
if (first) first.prev = element;
else this.last = element;
this.first = element;
}
shift() {
const element = this.first;
if (!element) return null;
if (this.last === element) {
this.first = null;
this.last = null;
} else {
this.first = element.next;
this.first.prev = null;
}
return element.item;
}
}
// Usage
const obj1 = { name: 'first' };
const obj2 = { name: 'second' };
const obj3 = { name: 'third' };
const list = new Dequeue();
list.push(obj1);
list.push(obj2);
list.unshift(obj3);
console.dir(list.pop());
console.dir(list.shift());
console.dir(list.shift());