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I'm trying to write an inversions counter that takes a list of integers as input and outputs the number of inversions. Since it's going to handle large lists, I'm using a divide and conquer recursive approach, but I'm getting the following error:

Traceback (most recent call last):
  File "C:\Users\Jonathan\Desktop\py.py", line 34, in <module>
    Inversions([1,2,3,4,5], 5)
  File "C:\Users\Jonathan\Desktop\py.py", line 13, in Inversions
    x = Inversions(numbers[:length/2 - 0.5], length/2-0.5)
TypeError: slice indices must be integers or None or have an __index__ method

Here is my code:

def Inversions(numbers, length):
    if length == 0:
        return 0
    else:
        if length%2 == 0:
            x = Inversions(numbers[:length/2], length/2)
            y = Inversions(numbers[length/2:], length/2)
            b = sorted(numbers[:length/2], length/2)
            c = sorted(numbers[length/2:], length/2)
            z = Split(b, c)
            return x+y+z
        elif length%2 == 1:
            x = Inversions(numbers[:length/2 - 0.5], length/2-0.5)
            y = Inversions(numbers[length/2 - 0.5:], length/2-0.5)
            b = sorted(numbers[:length/2 - 0.5], length/2-0.5)
            c = sorted(numbers[length/2 - 0.5:], length/2-0.5)
            z = Split(b, c)
            return x+y+z
def Split(first, second):
    i = 1
    j = 1
    d = []
    inversions = 0
    for k in range(1,len(b)+1):
        if b[i] < C[j]:
            d[k] = b[i]
            i += 1
        else:
            d[k] = c[j]
            inversions += len(b[i:])
            j += 1
    return inversions

Inversions([1,2,3,4,5], 5)
4

1 回答 1

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length是偶数，这会导致非整数浮点数。改用整数除法。

x = Inversions(numbers[:length // 2], length // 2)
于 2013-08-09T06:10:37.413 回答