Method push

interview/heap.js:11–15

(item)

    return this.arr.length-1
  }
  push(item){
    // 新增元素
    this.arr.push(item)
    this.shiftUp(this.arr.length-1)
  }
  shiftUp(k){
    let {arr,compare,parent} = this
    while(k>1 && compare(arr[k],arr[parent(k)])){