题目：
题解：
python
class DualHeap:
def __init__(self, k: int):
# 大根堆，维护较小的一半元素，注意 python 没有大根堆，需要将所有元素取相反数并使用小根堆
self.small = list()
# 小根堆，维护较大的一半元素
self.large = list()
# 哈希表，记录「延迟删除」的元素，key 为元素，value 为需要删除的次数
self.delayed = collections.Counter()
self.k = k
# small 和 large 当前包含的元素个数，需要扣除被「延迟删除」的元素
self.smallSize = 0
self.largeSize = 0
# 不断地弹出 heap 的堆顶元素，并且更新哈希表
def prune(self, heap: List[int]):
while heap:
num = heap[0]
if heap is self.small:
num = -num
if num in self.delayed:
self.delayed[num] -= 1
if self.delayed[num] == 0:
self.delayed.pop(num)
heapq.heappop(heap)
else:
break
# 调整 small 和 large 中的元素个数，使得二者的元素个数满足要求
def makeBalance(self):
if self.smallSize > self.largeSize + 1:
# small 比 large 元素多 2 个
heapq.heappush(self.large, -self.small[0])
heapq.heappop(self.small)
self.smallSize -= 1
self.largeSize += 1
# small 堆顶元素被移除，需要进行 prune
self.prune(self.small)
elif self.smallSize < self.largeSize:
# large 比 small 元素多 1 个
heapq.heappush(self.small, -self.large[0])
heapq.heappop(self.large)
self.smallSize += 1
self.largeSize -= 1
# large 堆顶元素被移除，需要进行 prune
self.prune(self.large)
def insert(self, num: int):
if not self.small or num <= -self.small[0]:
heapq.heappush(self.small, -num)
self.smallSize += 1
else:
heapq.heappush(self.large, num)
self.largeSize += 1
self.makeBalance()
def erase(self, num: int):
self.delayed[num] += 1
if num <= -self.small[0]:
self.smallSize -= 1
if num == -self.small[0]:
self.prune(self.small)
else:
self.largeSize -= 1
if num == self.large[0]:
self.prune(self.large)
self.makeBalance()
def getMedian(self) -> float:
return float(-self.small[0]) if self.k % 2 == 1 else (-self.small[0] + self.large[0]) / 2
class Solution:
def medianSlidingWindow(self, nums: List[int], k: int) -> List[float]:
dh = DualHeap(k)
for num in nums[:k]:
dh.insert(num)
ans = [dh.getMedian()]
for i in range(k, len(nums)):
dh.insert(nums[i])
dh.erase(nums[i - k])
ans.append(dh.getMedian())
return ans