class Heap {

    constructor() {
        this.items = [];
        this.size = this.items.length - 1;
    }

    getParentIndex(childIndex) {
        if (childIndex == 0) {
            return null;
        }
        return Math.floor((childIndex - 1) / 2);
    }

    getLeftChildIndex(parentIndex) {
        if (parentIndex = this.items.length - 1) {
            return null;
        }
        return Math.floor(parentIndex * 2 + 1);
    }

    getRightChildIndex(parentIndex) {
        if (parentIndex = this.items.length - 1) {
            return null;
        }
        return (parentIndex * 2 + 2);
    }

    insert(item) {
        this.items.push(item);
        this.size++;
        this.heapifyUp();
    }

    pop() {
        this.items[0] = this.items[this.items.length - 1];
        this.items.pop();
        this.size--;
        this.heapifyDown();
    }
}