How to Fix Find Median from Data Stream Errors

In this tutorial, you'll learn about How to Fix Find Median from Data Stream Errors. We cover key concepts, practical examples, and best practices.

Fix find median from data stream errors when two heaps not balanced or median calculated incorrectly.

Quick Fix

Wrong

def add(n):
    arr.append(n)
def median():
    arr.sort()
    return arr[len(arr)//2]

O(n log n) per median query. No streaming optimization.

Right

import heapq
class Median:
    def __init__(self):
        self.lo=[]  # max-heap via negative
        self.hi=[]  # min-heap
    def add(self,n):
        heapq.heappush(self.lo,-n)
        heapq.heappush(self.hi,-heapq.heappop(self.lo))
        if len(self.lo)<len(self.hi):
            heapq.heappush(self.lo,-heapq.heappop(self.hi))
    def median(self):
        if len(self.lo)>len(self.hi): return -self.lo[0]
        return (-self.lo[0]+self.hi[0])/2

add(1),add(2),median()->1.5,add(3),median()->2. O(log n) each.

Prevention

Two heaps: max-heap for lower half, min-heap for upper half. Balance sizes.

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