Problem -solving

maintain 3 indivual multiset：lower（Minimum kkk indivual数）、middle（Number in the middle）、upper（Most kkk indivual数）。

Insert operation

·if num≤max(lower)，Then lowerInsert num ·if num≥min(upper)，Then upper Insert num ·otherwise，exist middle Insert num if插入后，lower or upper There are more elements than k indivual，Then middle middle Transfer element

操作过程middlemaintain middle 的element和 sum

Delete operation

·设删除的element为 d ·d 一定存exist于 lower ormiddle or upper middle的一indivualor多indivual集合middle ·Choose one delete if删除后，lower or upper middle的element少于 k indivual，Then from middle middle Obtain element

操作过程middlemaintain middle 的element和 sum

average value操作

average value = sum/(m−2⋅k)sum / (m - 2\cdot k)sum/(m−2⋅k) （Take down）。

Code with problems：

class MKAverage:

    def __init__(self, m: int, k: int):
        self.m = m
        self.k = k
        self.list1 = []

    def addElement(self, num: int) -> None:
        self.list1.append(num)

    def calculateMKAverage(self) -> int:
        if len(self.list1) < self.m:
            return -1
        else:
            list2 = self.list1[-1:-self.m-1:-1]
            list2 = sorted(list2)
            list2 = list2[self.k:len(list2) - self.k]
        return sum(list2) // len(list2)

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