Although Wikipedia mentions that JavaScript has native support for deque operations via its Array class/prototype (push, pop, shift, unshift), this does not give the optimal time efficiency, which becomes important the larger your dataset is. If we regard the optimal time efficiency a requirement for a deque implementation, then JavaScript does not have a native implementation.
If you need good performance for larger datasets, you will want to write your own implementation. You can go for a doubly linked list, where you just need two "pointers". It should be said that in JavaScript we don't really speak of pointers, but of objects. Variables or properties that get an object as value, are in fact references in JavaScript.
Alternatively, you can go for a circular array. Since in JavaScript standard Arrays are not guaranteed to be consecutive arrays as for example is the case in C, you don't really need to use an Array instance for that. A plain object (or Map) will do.
So here are two possible implementations:
Doubly Linked List
class Deque {
constructor() {
this.front = this.back = undefined;
}
addFront(value) {
if (!this.front) this.front = this.back = { value };
else this.front = this.front.next = { value, prev: this.front };
}
removeFront() {
let value = this.peekFront();
if (this.front === this.back) this.front = this.back = undefined;
else (this.front = this.front.prev).next = undefined;
return value;
}
peekFront() {
return this.front && this.front.value;
}
addBack(value) {
if (!this.front) this.front = this.back = { value };
else this.back = this.back.prev = { value, next: this.back };
}
removeBack() {
let value = this.peekBack();
if (this.front === this.back) this.front = this.back = undefined;
else (this.back = this.back.next).back = undefined;
return value;
}
peekBack() {
return this.back && this.back.value;
}
}
// demo
let deque = new Deque;
console.log(deque.peekFront()); // undefined
deque.addFront(1);
console.log(deque.peekBack()); // 1
deque.addFront(2);
console.log(deque.removeBack()); // 1
deque.addFront(3);
deque.addFront(4);
console.log(deque.peekBack()); // 2
deque.addBack(5);
deque.addBack(6);
console.log(deque.peekBack()); // 6
console.log(deque.removeFront()); // 4
console.log(deque.removeFront()); // 3
console.log(deque.removeFront()); // 2
console.log(deque.removeFront()); // 5
console.log(deque.removeFront()); // 6
console.log(deque.removeFront()); // undefined
Circular "Array"
class Deque {
constructor() {
this.data = {}; // Or Array, but that really does not add anything useful
this.front = 0;
this.back = 1;
this.size = 0;
}
addFront(value) {
if (this.size >= Number.MAX_SAFE_INTEGER) throw "Deque capacity overflow";
this.size++;
this.front = (this.front + 1) % Number.MAX_SAFE_INTEGER;
this.data[this.front] = value;
}
removeFront() {
if (!this.size) return;
let value = this.peekFront();
this.size--;
delete this.data[this.front];
this.front = (this.front || Number.MAX_SAFE_INTEGER) - 1;
return value;
}
peekFront() {
if (this.size) return this.data[this.front];
}
addBack(value) {
if (this.size >= Number.MAX_SAFE_INTEGER) throw "Deque capacity overflow";
this.size++;
this.back = (this.back || Number.MAX_SAFE_INTEGER) - 1;
this.data[this.back] = value;
}
removeBack() {
if (!this.size) return;
let value = this.peekBack();
this.size--;
delete this.data[this.back];
this.back = (this.back + 1) % Number.MAX_SAFE_INTEGER;
return value;
}
peekBack() {
if (this.size) return this.data[this.back];
}
}
// demo
let deque = new Deque;
console.log(deque.peekFront()); // undefined
deque.addFront(1);
console.log(deque.peekBack()); // 1
deque.addFront(2);
console.log(deque.removeBack()); // 1
deque.addFront(3);
deque.addFront(4);
console.log(deque.peekBack()); // 2
deque.addBack(5);
deque.addBack(6);
console.log(deque.peekBack()); // 6
console.log(deque.removeFront()); // 4
console.log(deque.removeFront()); // 3
console.log(deque.removeFront()); // 2
console.log(deque.removeFront()); // 5
console.log(deque.removeFront()); // 6
console.log(deque.removeFront()); // undefined
Methods will return undefined, when an attempt is made to retrieve a value from an empty deque.
In my tests the linked list solution came out as the winner as the data set grows. For small datasets sizes, the native array may turn out to be best. But it also depends on the engine and the data type that the deque elements have: the results for integers are different from the results for objects or strings. So I would advise to do some benchmarking on your actual data and deque manipulations to see which implementation will be best for your case.
push(),pop(),shift(),unshift()as well as standard index accessing should give you all the tools you need. – Burgundydequeand justdefault JS arraydo the job ? – Diatropismdefault JS arrayallow random access to data whiledequewill not allow to add,modify or delete from the middle just from the end – Diatropismmap(), ...). – Burgundydeque based arraybut let me being greedy how to implementdeque based objectalso using class and constructor ? – Diatropismtrincotanswer. could you read my question post again I added more details – Diatropismitemsinstead ofdata, but after all it's quite similar. No linked lists in either implementation. – Purr