"use strict";

/**

* TripleStack class holds 3 stacks in one array. This is done by interleaving

* the values from the 3 indexes, so the first items are at 0, 1 and 2 and

* subsequent items are every 3 places from those. This class takes advantage

* of the fact that JavaScript arrays are dynamic and doesn't hold the stacks

* to any size. It doesn't reduce the size of the underlying array when items

* are popped but that could easily be added.

*

* Time: push O(1), pop O(1), peek O(1)

* Additional space: push O(1), pop O(1), peek O(1)

*/

export class TripleStack {

constructor() {

this._array = [];

this._lengths = [0, 0, 0];

}

_getLength(stack) {

return this._lengths[stack - 1];

}

push(stack, value) {

let idx = this._getLength(stack) * 3 + stack - 1;

this._array[idx] = value;

++this._lengths[stack - 1];

}

pop(stack) {

let length = this._getLength(stack),

value;

if (length > 0) {

let idx = (length - 1) * 3 + stack - 1;

value = this._array[idx];

this._array[idx] = undefined;

--this._lengths[stack - 1];

}

return value;

}

peek(stack) {

let length = this._getLength(stack),

value;

if (length > 0) {

let idx = (length - 1) * 3 + stack - 1;

value = this._array[idx];

}

return value;

}

isEmpty(stack) {

return this._getLength(stack) === 0;

}

}

const myTripleStack = new TripleStack();

myTripleStack.push(3, 3);

myTripleStack.push(3, 3);

myTripleStack.push(3, 3);

myTripleStack.push(1, 1);