这也是Google面试题
股市上一个股票的价格从开市开始是不停的变化的，需要开发一个系统，给定一个股票，它能实时显示从开市到当前时间的这个股票的价格的中位数（中值）。
用双堆存储，一个大根堆，一个小根堆，则Inert为O(logn)，Median为O(1)
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import java.util.*;
public class FindMedian {
private static PriorityQueue<Integer> maxHeap, minHeap;
FindMedian(int n) {
Comparator<Integer> revCmp = new Comparator<Integer>() {
@Override
public int compare(Integer left, Integer right) {
return right.compareTo(left);
}
};
// Or you can use Collections' reverseOrder method as follows.
// Comparator<Integer> revCmp = Collections.reverseOrder();
maxHeap = new PriorityQueue<Integer>(n, revCmp);
minHeap = new PriorityQueue<Integer>(n);
}
public void addNewNumber(int randomNumber) {
if (maxHeap.size() == minHeap.size()) {
if ((minHeap.peek() != null) && randomNumber > minHeap.peek()) {
maxHeap.offer(minHeap.poll());
minHeap.offer(randomNumber);
} else {
maxHeap.offer(randomNumber);
}
}
else { // trick
if(randomNumber < maxHeap.peek()) {
minHeap.offer(maxHeap.poll());
maxHeap.offer(randomNumber);
}
else {
minHeap.offer(randomNumber);
}
}
}
public int getMedian() {
if (maxHeap.isEmpty()) return minHeap.peek();
else if (minHeap.isEmpty()) return maxHeap.peek();
if (maxHeap.size() == minHeap.size()) {
return (minHeap.peek() + maxHeap.peek()) / 2;
} else if (maxHeap.size() > minHeap.size()) {
return maxHeap.peek();
} else {
return minHeap.peek();
}
}
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
int n = in.nextInt();
FindMedian fm = new FindMedian(n);
for (int i = 0; i < n; i++) {
int num = in.nextInt();
fm.addNewNumber(num);
}
System.out.println(fm.getMedian());
}
}
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