max-binary-heap.js

export default class MaxBinaryHeap {
  constructor() {
    this.values = []
  }
  insert(val) {
    this.values.push(val)
    this.bubbleUp()
  }
  bubbleUp() {
    let idx = this.values.length - 1
    let element = this.values[idx]
    while (idx > 0) {
      let parentIdx = Math.floor((idx - 1) / 2)
      let parent = this.values[parentIdx]
      if (element <= parent) break
      this.values[parentIdx] = element
      this.values[idx] = parent
      idx = parentIdx
    }
  }
  /**
   * Extract max (root node) includes three steps
   * 
   * - Remove the root
   * - Replace with the most recently added
   * - Adjust (sink down)
   */

  extractMax() {
    const max = this.values[0]
    const end = this.values.pop()
    if (this.values.length > 0) {
      this.values[0] = end
      this.sinkDown()
    }
    return max
  }
  /**
   * The procedure for deleting the root from the heap (effectively extracting the maximum element in a max-heap 
   * or the minimum element in a min-heap) and restoring the properties is called down-heap
   */
  sinkDown() {
    let idx = 0;
    const length = this.values.length;
    const element = this.values[0];
    while (true) {
      let leftChildIdx = 2 * idx + 1;
      let rightChildIdx = 2 * idx + 2;
      let leftChild, rightChild;
      let swap = null;

      if (leftChildIdx < length) {
        leftChild = this.values[leftChildIdx];
        if (leftChild > element) {
          swap = leftChildIdx;
        }
      }
      if (rightChildIdx < length) {
        rightChild = this.values[rightChildIdx];
        if (
          (swap === null && rightChild > element) ||
          (swap !== null && rightChild > leftChild)
        ) {
          swap = rightChildIdx;
        }
      }
      if (swap === null) break;
      this.values[idx] = this.values[swap];
      this.values[swap] = element;
      idx = swap;
    }
  }
}