LeetCode-in-All

295. Find Median from Data Stream

Hard

The median is the middle value in an ordered integer list. If the size of the list is even, there is no middle value and the median is the mean of the two middle values.

Implement the MedianFinder class:

Example 1:

Input

["MedianFinder", "addNum", "addNum", "findMedian", "addNum", "findMedian"]
[[], [1], [2], [], [3], []]

Output: [null, null, null, 1.5, null, 2.0]

Explanation:

MedianFinder medianFinder = new MedianFinder();
medianFinder.addNum(1); // arr = [1]
medianFinder.addNum(2); // arr = [1, 2]
medianFinder.findMedian(); // return 1.5 (i.e., (1 + 2) / 2)
medianFinder.addNum(3); // arr[1, 2, 3]
medianFinder.findMedian(); // return 2.0 

Constraints:

Follow up:

Solution

import scala.collection.mutable

class MedianFinder() {
    private val maxHeap = mutable.PriorityQueue.empty[Int]
    private val minHeap = mutable.PriorityQueue.empty[Int](Ordering.Int.reverse)

    def addNum(num: Int): Unit = {
        maxHeap += num
        minHeap += maxHeap.dequeue()

        if (maxHeap.size < minHeap.size)
            maxHeap += minHeap.dequeue()
    }

    def findMedian(): Double = {
        if (maxHeap.size > minHeap.size)
            maxHeap.head
        else
            (maxHeap.head + minHeap.head).toDouble / 2
    }
}

/*
 * Your MedianFinder object will be instantiated and called as such:
 * var obj = new MedianFinder()
 * obj.addNum(num)
 * var param_2 = obj.findMedian()
 */