Woodstock Blog

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[Question] Median in a Stream of Integers



Given that integers are read from a data stream. Find median of elements read so for in efficient way.

For simplicity assume there are no duplicates. For example, let us consider the stream 5, 15, 1, 3 … The stream of output is 5, 10, 1, 4 …


we can use a max heap on left side to represent elements that are less than effective median, and a min heap on right side to represent elements that are greater than effective median.

After processing an incoming element, the number of elements in heaps differ utmost by 1 element. source

So we know that java.util.PriorityQueue is a max-heap. The only question is, how to implement a min-heap? Someone sugests writing your own customized Comparator:

you use two instances of a java.util.PriorityQueue containing the same elements? The first instance would be passed a comparator which puts the maximum at the head, and the second instance would use a comparator which puts the minimum at the head.