****题目：
有一个源源不断地吐出整数的数据流， 假设你有足够的空间来保存吐出的数。 请设计一个名叫
MedianHolder的结构，MedianHolder可以随时取得之前吐出所有数的中位数

****要求：
1． 如果MedianHolder已经保存了吐出的N个数， 那么任意时刻将一个新数加入到MedianHolder
的过程， 其时间复杂度是O(logN)。
2． 取得已经吐出的N个数整体的中位数的过程， 时间复杂度为O(1)。

public static class MedianHolder {
        private PriorityQueue<Integer> maxHeap = new PriorityQueue<Integer>(new MaxHeapComparator());
        private PriorityQueue<Integer> minHeap = new PriorityQueue<Integer>(new MinHeapComparator());

        private void modifyTwoHeapsSize() {
            if (this.maxHeap.size() == this.minHeap.size() + 2) {
                this.minHeap.add(this.maxHeap.poll());
            }
            if (this.minHeap.size() == this.maxHeap.size() + 2) {
                this.maxHeap.add(this.minHeap.poll());
            }
        }

        public void addNumber(int num) {
            if (this.maxHeap.isEmpty()) {
                this.maxHeap.add(num);
                return;
            }
            if (this.maxHeap.peek() >= num) {
                this.maxHeap.add(num);
            } else {
                if (this.minHeap.isEmpty()) {
                    this.minHeap.add(num);
                    return;
                }
                if (this.minHeap.peek() > num) {
                    this.maxHeap.add(num);
                } else {
                    this.minHeap.add(num);
                }
            }
            modifyTwoHeapsSize();
        }

        public Integer getMedian() {
            int maxHeapSize = this.maxHeap.size();
            int minHeapSize = this.minHeap.size();
            if (maxHeapSize + minHeapSize == 0) {
                return null;
            }
            Integer maxHeapHead = this.maxHeap.peek();
            Integer minHeapHead = this.minHeap.peek();
            if (((maxHeapSize + minHeapSize) & 1) == 0) {
                return (maxHeapHead + minHeapHead) / 2;
            }
            return maxHeapSize > minHeapSize ? maxHeapHead : minHeapHead;
        }

    }


//构建大根堆
public static class MaxHeapComparator implements Comparator<Integer> {
        @Override
        public int compare(Integer o1, Integer o2) {
            if (o2 > o1) {
                return 1;
            } else {
                return -1;
            }
        }
    }

//构建小根堆
public static class MinHeapComparator implements Comparator<Integer> {
        @Override
        public int compare(Integer o1, Integer o2) {
            if (o2 < o1) {
                return 1;
            } else {
                return -1;
            }
        }
    }