我正在尝试返回一系列流数字的运行中位数.为此,我使用max-heap(存储系列下半部分的值)和min-heap(将值存储在系列的上半部分).

特别是我正在使用来自heapq模块(https://docs.python.org/2/library/heapq.html)的Python(2.0)内置最小堆数据结构.要构建最大堆,我只需使用我需要的数字的负数进入我的堆.

我的Python代码如下：

import heapq

maxh = []
minh = []
vals=[1,2,3,4,5,6,7,8,9,10]
for val in vals:

    # Initialize the data-structure and insert/push the 1st streaming value
    if not maxh and not minh:
        heapq.heappush(maxh,-val)
        print float(val)
    elif maxh:

        # Insert/push the other streaming values
        if val>-maxh[0]:
            heapq.heappush(minh,val)
        elif val<-maxh[0]:
            heapq.heappush(maxh,-val)

        # Calculate the median
        if len(maxh)==len(minh):
            print float(-maxh[0]+minh[0])/2
        elif len(maxh)==len(minh)+1:
            print float(-maxh[0])
        elif len(minh)==len(maxh)+1:
            print float(minh[0])

        # If min-heap and max-heap grow unbalanced we rebalance them by
        # removing/popping one element from a heap and inserting/pushing
        # it into the other heap, then we calculate the median
        elif len(minh)==len(maxh)+2:
            heapq.heappush(maxh,-heapq.heappop(minh))
            print float(-maxh[0]+minh[0])/2
        elif len(maxh)==len(minh)+2:
            heapq.heappush(minh,-heapq.heappop(maxh))
            print float(-maxh[0]+minh[0])/2

下面是我为检查代码而构建的测试用例的完整列表：

vals=[1,2,3,4,5,6,7,8,9,10] # positive numbers, increasing series
vals=[10,9,8,7,6,5,4,3,2,1] # positive numbers, decreasing series
vals=[10,9,11,8,12,7,13,6,14,5] # positive numbers, jumping series (keeping
                                # heaps balanced)

vals=[-10,-9,-8,-7,-6,-5,-4,-3,-2,-1] # negative numbers, increasing series
vals=[-1,-2,-3,-4,-5,-6,-7,-8,-9,-10] # negative numbers, decreasing series
vals=[-10,-9,-11,-8,-12,-7,-13,-6,-14,-5] # negative numbers
                                          # jumping series (keeping heaps
                                          # balanced)

vals=[-5,-4,-3,-2,-1,0,1,2,3,4,5] # mixed positive-negative numbers,
                                  # increasing series
vals=[5,4,3,2,1,0,-1,-2,-3,-4,-5] # mixed positive-negative numbers,
                                  # decreasing series
vals=[0,-1,1,-2,2,-3,3,-4,4,-5,5] # mixed positive-negative numbers,
                                  # jumping series (keeping heaps balanced)

我的代码对我来说似乎没问题但我无法通过在线评判(https://www.hackerrank.com/challenges/ctci-find-the-running-median/problem)传递10个测试用例中的4个.

你有什么提示吗？

解决方法:

问题出在这里：

    # Insert/push the other streaming values
    if val>-maxh[0]:
        heapq.heappush(minh,val)
    elif val<-maxh[0]:
        heapq.heappush(maxh,-val)

如果val == maxh [0],则该项永远不会被推送到任何一个堆上.您应该能够通过测试用例[1,1,2]显示错误.

一个简单的解决方案是：

    # Insert/push the other streaming values
    if val >= -maxh[0]:
        heapq.heappush(minh,val)
    else
        heapq.heappush(maxh,-val)