计算逆序数对

python语言：

#-*- coding:utf-8 -*-
#import pdb

def sort_count(data):
"""
using merge sort and count inversion
"""
global count
count = 0
def merge_sort(data):
global count
if len(data)<2:
return data

left = merge_sort(data[:(len(data)//2)])
right = merge_sort(data[(len(data)//2):])
idx_left = idx_right = 0
result = []
while idx_left < len(left) and idx_right < len(right):
if left[idx_left] <= right[idx_right]:
result.append(left[idx_left])
idx_left += 1
else:
result.append(right[idx_right])
idx_right += 1
count += len(left)-idx_left
while idx_left < len(left):
result.append(left[idx_left])
idx_left += 1

while idx_right < len(right):
result.append(right[idx_right])
idx_right += 1
return result

sorted_data = merge_sort(data)

return count

class Ivrs_num(object):
def __init__(self, filename):
self.count = 0
self.filename = filename

def inverse_count(self):
data = self.load_txt()
def merge_sort(data):

if len(data)<2:
return data

left = merge_sort(data[:(len(data)//2)])
right = merge_sort(data[(len(data)//2):])
idx_left = idx_right = 0
result = []
while idx_left < len(left) and idx_right < len(right):
if left[idx_left] <= right[idx_right]:
result.append(left[idx_left])
idx_left += 1
else:
result.append(right[idx_right])
idx_right += 1
self.count += len(left)-idx_left
while idx_left < len(left):
result.append(left[idx_left])
idx_left += 1

while idx_right < len(right):
result.append(right[idx_right])
idx_right += 1
return result
merge_sort(data)
return self.count

def load_txt(self):
int_list = []
with open(self.filename) as f:
for line in f:
int_list.append(int(line))
return int_list

if __name__ == '__main__':

m = Ivrs_num('IntegerArray.txt')

print(m.inverse_count())



cpp版：
#include <iostream>

//Inversion Pair

int merge_sort(int a[], int len)
{
if(len<2) return 0;
int left[len/2],right[len-len/2];
int i,j,index,inver=0;
for(i=0;i<len/2;i++)
{
left[i]=a[i];
}
for(i=len/2,j=0;i<len;i++,j++)
{
right[j]=a[i];
}
inver += merge_sort(left, len/2);
inver += merge_sort(right, len-len/2);
index=0;
i=0;
j=0;
while(i<len/2 && j<(len-len/2))
{
if(left[i] <= right[j])
{
a[index]=left[i];
index++;
i++;
}
else
{
a[index]=right[j];
j++;
index++;
inver += len/2 - i;
}
}
while(i<len/2)
{
a[index]=left[i];
index++;
i++;
}
while(j<(len-len/2))
{
a[index]=right[j];
index++;
j++;
}
return inver;
}

int main()
{
int len;
std::cin>>len;
int array[len],i;
for(i=0;i<len;i++)
{
std::cin>>array[i];
}

std::cout<<merge_sort(array,len);
/*
int array[]={4,2,6,1,5,3,0};
int count=0;
std::cout<<merge_sort(array,7)<<std::endl;
int i=0;
for(i=0;i<7;i++)
{
std::cout<<array[i]<<" ";
}
*/
return 0;
}