优先队列问题。 在 while 循环中未定义优先级。 如何将元素排入队列？

Question

doing a priority queue as a min-heap in javascript. console keeps returning priority is undefined in the while loop. what is the problem? / how to enqueue element to queue?

 //min-heap class PriorityQueue { constructor(){ this.values = []; } enqueue(value, priority){ let newNode = new Node(value, priority); this.values.push(newNode); this.bubbleUp(); } bubbleUp(){ let childIndex = this.values.length - 1; let parentIndex = Math.floor((childIndex - 1) / 2); let childElement = this.values[childIndex].priority; let parentElement = this.values[parentIndex].priority; while(childElement < parentElement){ let temp = this.values[childIndex]; this.values[childIndex] = this.values[parentIndex]; this.values[parentIndex] = temp; childIndex = parentIndex; parentIndex = Math.floor((childIndex - 1) / 2); } } }

Answer 1

A few issues in your bubbleUp method:

• The while loop never updates the variables that are compared in the loop condition.
• The processing should detect when parentIndex is no longer valid, ie when childIndex is the root, and then exit.

Here is a correction:

  bubbleUp(){
    let childIndex = this.values.length - 1;
    let parentIndex = Math.floor((childIndex - 1) / 2);

    while (childIndex > 0 && this.values[childIndex].priority < this.values[parentIndex].priority){
      let temp = this.values[childIndex];
      this.values[childIndex] = this.values[parentIndex];
      this.values[parentIndex] = temp;

      childIndex = parentIndex;
      parentIndex = Math.floor((childIndex - 1) / 2);
    }
  }

For full implementations, have a look at Efficient way to implement Priority Queue in Javascript? , where I have also posted my preferred implementation .