295. Find Median from Data Stream题test case过不了的原因

请教大神，不知道17-22行哪里出了问题，总是取不到奇数情况的中间数，用的test case是

["MedianFinder","addNum","findMedian","addNum","findMedian","addNum","findMedian","addNum","findMedian","addNum","findMedian"][[],[-1],[],[-2],[],[-3],[],[-4],[],[-5],[]]

代码如下：

1. class MedianFinder {
   
2.     PriorityQueue<Integer> pq;
   
3.     /** initialize your data structure here. */
   
4.     public MedianFinder() {
   
5.         pq = new PriorityQueue<>();
   
6.     }
   
7.    
   
8.     public void addNum(int num) {
   
9.         pq.add(num);
   
10.     }
    
11.    
    
12.     public double findMedian() {
    
13.         int n = pq.size();
    
14.         double res = 0.0;
    
15.         Iterator iter = pq.iterator();
    
16.         Integer tmp = 0;
    
17.         if (n % 2 != 0) {
    
18.             for (int i = 0; i < n/2; i++) {
    
19.                 iter.next();
    
20.             }
    
21.             tmp = (Integer) iter.next();
    
22.             res = (double) tmp;
    
23.         } else {
    
24.             for (int i = 0; i < n/2; i++) {
    
25.                 tmp = (Integer) iter.next();
    
26.             }
    
27.             Integer x = (Integer) iter.next();
    
28.             res = ((double) tmp + (double) x)/2;
    
29.         }
    
30.         return res;
    
31.     }
    
32. }
    
33. 
    
34. /**
    
35. * Your MedianFinder object will be instantiated and called as such:
    
36. * MedianFinder obj = new MedianFinder();
    
37. * obj.addNum(num);
    
38. * double param_2 = obj.findMedian();
    
39. */

复制代码

Java的pq iterator 不代表顺序，底层的结构是数组，只具有一定的堆序性，整体不算是有序的。

https://docs.oracle.com/javase/8.../PriorityQueue.html#iterator--

“
java.util
Class PriorityQueue&lt;E&gt;
...
public Iterator&lt;E&gt; iterator()
... The iterator does not return the elements in any particular order.
“

所以用priority queue + iterator在这里意义不大?