ds-algo-study/DS-n-Algos/Misc/heaps_project/lib/max_heap.js

Just experimenting with publishing a package

class MaxHeap {
  constructor() {
    this.array = [null];
  }

  getParent(idx) {
    return Math.floor(idx / 2);
  }

  getLeftChild(idx) {
    return idx * 2;
  }

  getRightChild(idx) {
    return idx * 2 + 1;
  }

  siftUp(idx) {
    if (idx === 1) return;
    let parentIdx = this.getParent(idx);
    if (this.array[parentIdx] < this.array[idx]) {
      [this.array[parentIdx], this.array[idx]] = [
        this.array[idx],
        this.array[parentIdx]
      ];
      this.siftUp(parentIdx);
    }
  }

  insert(val) {
    this.array.push(val);
    this.siftUp(this.array.length - 1);
  }

  siftDown(idx) {
    let leftIdx = this.getLeftChild(idx);
    let rightIdx = this.getRightChild(idx);
    let left = this.array[leftIdx];
    let right = this.array[rightIdx];
    if (left === undefined) left = -Infinity;
    if (right === undefined) right = -Infinity;
    if (this.array[idx] > left && this.array[idx] > right) return;
    let swapIdx = left < right ? rightIdx : leftIdx;

    [this.array[idx], this.array[swapIdx]] = [
      this.array[swapIdx],
      this.array[idx]
    ];
    this.siftDown(swapIdx);
  }

  deleteMax() {
    if (this.array.length === 2) return this.array.pop();
    if (this.array.length < 2) return null;
    let max = this.array[1];
    this.array[1] = this.array.pop();
    this.siftDown(1);
    return max;
  }
}

module.exports = {
  MaxHeap
};