Question

我已经实现了合并排序，以及排序，我希望它能够计算原始数组中WP-Club-Manager Plugin的数量。

以下是我实施它的尝试，由于某种原因，它无法正确计算反转次数。

例如，(6, [1, 2, 3, 4])应返回def mergeSort(alist): count = 0 if len(alist)>1: mid = len(alist)//2 lefthalf = alist[:mid] righthalf = alist[mid:] mergeSort(lefthalf) mergeSort(righthalf) i=0 j=0 k=0 while i < len(lefthalf) and j < len(righthalf): if lefthalf[i] < righthalf[j]: alist[k]=lefthalf[i] i=i+1 else: alist[k]=righthalf[j] count +=len(lefthalf[i:]) j=j+1 k=k+1 while i < len(lefthalf): alist[k]=lefthalf[i] i=i+1 k=k+1 while j < len(righthalf): alist[k]=righthalf[j] j=j+1 k=k+1 return count, alist。

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Answer 1

主要问题不包括左右分类的数量。

def mergeSort(alist):
    count = 0
    leftcount = 0
    rightcount = 0
    blist = [] 
    if len(alist) > 1:
       mid = len(alist) // 2
       lefthalf = alist[:mid]
       righthalf = alist[mid:]
       leftcount, lefthalf = mergeSort(lefthalf)
       rightcount, righthalf = mergeSort(righthalf)

       i = 0
       j = 0

       while i < len(lefthalf) and j < len(righthalf):
         if lefthalf[i] < righthalf[j]:
             blist.append(lefthalf[i])
             i += 1
         else:
             blist.append(righthalf[j])
             j += 1
             count += len(lefthalf[i:])

       while i < len(lefthalf):
          blist.append(lefthalf[i])
          i += 1

       while j < len(righthalf):
          blist.append(righthalf[j])
          j += 1
    else:
        blist = alist[:]

    return count + leftcount + rightcount, blist

Answer 2

您的函数返回（反转，sortedlist）元组。但是你的内部递归调用完全忽略了这一点，所以你计算在顶层以下的任何反转都只是被抛到一边而不计算在内。

  lc, lefthalf = mergeSort(alist[:mid])
  rc, righthalf = mergeSort(alist[mid:])
  count = count + lc + rc

如果你与同学分享，你可以使用：

def count_inversions(data):
    count, result = mergeSort(data)
    return count

test_cases = [
    (3, [1,3,5,2,4,6]),
    (590, [37, 7, 2, 14, 35, 47, 10, 24, 44, 17, 34, 11, 16, 48, 1, 39, 6, 33, 43, 26, 40, 4, 28, 5, 38, 41, 42, 12, 13, 21, 29, 18, 3, 19, 0, 32, 46, 27, 31, 25, 15, 36, 20, 8, 9, 49, 22, 23, 30, 45]),
    (2372, [4, 80, 70, 23, 9, 60, 68, 27, 66, 78, 12, 40, 52, 53, 44, 8, 49, 28, 18, 46, 21, 39, 51, 7, 87, 99, 69, 62, 84, 6, 79, 67, 14, 98, 83, 0, 96, 5, 82, 10, 26, 48, 3, 2, 15, 92, 11, 55, 63, 97, 43, 45, 81, 42, 95, 20, 25, 74, 24, 72, 91, 35, 86, 19, 75, 58, 71, 47, 76, 59, 64, 93, 17, 50, 56, 94, 90, 89, 32, 37, 34, 65, 1, 73, 41, 36, 57, 77, 30, 22, 13, 29, 38, 16, 88, 61, 31, 85, 33, 54]),
]

def validate():
    for expected, data in test_cases:
        answer = count_inversions(data)
        if answer != expected:
            print "FAILED VALIDATION -- actual:", answer, "expected:", expected, "data:", data

validate()

计算合并排序中的反转次数

2 个答案: