java - Java实现优先级队列的问题

Question

我目前的优先级队列存在问题。当我测试我的方法时，我收到一条错误消息，指出我的队列没有返回最高优先级。我已逐步完成，但我不明白为什么 Poll 或 Offer 方法会导致此问题。任何帮助，将不胜感激。谢谢

public class HeapArrayQueue <E extends Comparable<? super E> > extends AbstractQueue <E> { 

@SuppressWarnings("unchecked") 
private E[] data = (E[])(new Comparable[7]);
private int count = 0;
private int front = 0;
public int size() {
    return count;
}

public boolean isEmpty() { 
    return size() == 0; 
}

public E poll() {
     if (isEmpty())
        return null;
    else {
        E ans = data[front ];
        front = (front+1);       
        return ans;
    }
}


public boolean offer(E element) {
    if (element == null)return false;
    else {
        ensureCapacity();
        data[count] = element;
        bubbleUpFromIndex(count);
        count++;
        return true;
    }
}

private void bubbleUpFromIndex(int nodeIndex) {
     if (nodeIndex != 0){
         int parent = (nodeIndex -1) / 2;
         if (data[nodeIndex].compareTo(data[parent]) > 0){
             swap(nodeIndex, parent);
             bubbleUpFromIndex(parent);
         }
    }
}

private void swap(int from, int to) {
    E temp = data[from];
    data[from] = data[to];
    data[to] = temp;
}

private void ensureCapacity() {
    if (count == data.length) {
        @SuppressWarnings("unchecked") 
        E[] newData = (E[])new Comparable[data.length * 2];

        for (int loop = 0; loop < count; loop++) {
            newData[loop] = data[loop];
        }
        data = newData;
    }
    return;
}

public Iterator<E> iterator() { 
    return null; 
}
}

测试失败

@Test
public void QueueRespectsPriority() {
    nonEmptyQueue.offer(t1);
    assertEquals("Queue should return element with highest priority", t1, nonEmptyQueue.poll());
}

Answer 1

我在 vic 做 comp103 吗？看起来与我现在正在做的事情非常相似。

我看到的第一件事是您没有在民意调查中保留正确的优先级。这里(伪代码是我的方法)

public E poll(){
if (count = 0) return null
E item = root   // We are returning the root node so store it as a var
root = end      // place the end item in root position
end = null      // set end item to null
count--         // subtract count
sinkDown(0)     // Call sink down to restore ordering
return item     // return item
}