class MedianFinder {

Queue<Integer> A,B;

/** initialize your data structure here. */

public MedianFinder() {

A = new PriorityQueue<>();

B = new PriorityQueue<>((a, b) -> b - a);

}

public void addNum(int num) {

// 判断条件A和B可以对换位置，但是输出也应该跟着变

if (A.size() != B.size()) {

B.add(num);

A.add(B.poll());

} else {

A.add(num);

B.add(A.poll());

}

}

public double findMedian() {

if (A.isEmpty()) return B.peek();

if (B.isEmpty()) return A.peek();

return A.size() != B.size() ? B.peek() : (A.peek() + B.peek()) / 2.0;

}

}