Question

import sys

def get_number_of_inversions(a, b, left, right):
    number_of_inversions = 0
    if right - left <= 1:
        return number_of_inversions
    ave = (left + right) // 2
    number_of_inversions += get_number_of_inversions(a, b, left, ave)
    number_of_inversions += get_number_of_inversions(a, b, ave, right)
    #write your code here
    return number_of_inversions

if __name__ == '__main__':
    input = sys.stdin.read()
    n, *a = list(map(int, input.split()))
    b = n * [0]
    print(get_number_of_inversions(a, b, 0, len(a)))

此代码只能在“在此处编写代码”区域中实现

以及我整天想做的事情：

i=left
j=ave
k=left
temp_num=0
while i<ave and j<right:
    if a[i]<=a[j]:
        b[k]=a[i]
        i+=1
    else:
        b[k]=a[j]
        j+=1
        temp_num += (ave-i)
    k+=1

number_of_inversions+=temp_num

第二次尝试不那么聪明：

left=a[:ave]
right=a[ave:]

result = list()
i,j = 0,0
inv_count = 0
while i < len(left) and j < len(right):
    if left[i] < right[j]:
        result.append(left[i])
        i += 1
    elif right[j] < left[i]:
        result.append(right[j])
        j += 1
        inv_count += (len(left)-i)
result += left[i:]
result += right[j:]

number_of_inversions +=inv_count

对我来说最有问题的是：

程序开始运行时使用比实际大的正确索引首先进行递归调用程序不返回子数组而只返回反转数

请给我一些如何实现该代码的建议

Answer 1

我不确定你要做什么但问题可能在这里right - left <= 1 我认为它应该是right <= left

实现合并反转查找器

1 个答案: