algorithmpool/src/dspool/priority_queue.js

A pool of algorithms and data-structures for geeks

export class priorityQueue {
    constructor(){
        this.elements = [];
        this.offset = 0;
        this.priorities = {};
    }

    length(){
        return this.elements.length - this.offset;
    }

    isEmpty(){
        return this.length() === 0;
    }

    toArray(){
        const arr = [];
        if (this.isEmpty()) {
            return arr;
        }
        const pKeys = Object.keys(this.priorities);
        for (let i = offset; i < pKeys.length; i += 1) {
            arr.push(this.elements[this.priorities[pKeys[i]]]);
        }
        return arr;
    };

    clear() {
        this.elements = [];
        this.offset = 0;
        this.priorities = {};
    };

    front(){
        if (!this.isEmpty()) {
            const pKeys = Object.keys(this.priorities);
            const firstIndex = this.priorities[pKeys[this.offset]];
            return this.elements[firstIndex];
        }
        return null;
    };

    back(){
        if (!this.isEmpty()) {
            const pKeys = Object.keys(this.priorities);
            const lastIndex = this.priorities[pKeys[pKeys.length - 1]];
            return this.elements[lastIndex];
        }
        return null;
    };

    enqueue(el, priority){
        if (Number.isNaN(+priority) || priority < 1) {
            throw new Error('priority should be a positive number');
        }
        this.elements.push(el);
        this.priorities[priority] = this.elements.length - 1;
    };

    dequeue(){
        if (!this.isEmpty()) {
            const first = front();
            this.offset += 1;
            if (this.offset * 2 >= this.elements.length) {
                const pKeys = Object.keys(this.priorities);
                const els = [];
                const prs = {};
                for (let i = this.offset; i < this.elements.length; i += 1) {
                    els.push(this.elements[this.priorities[pKeys[i]]]);
                    prs[this.priorities[i]] = els.length - 1;
                }
                this.priorities = prs;
                this.elements = els;
                this.offset = 0;
            }
            return first;
        }
        return null;
    };

}