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We're a place where coders share, stay up-to-date and grow their careers. # Counting Inversion by piggybacking on Merge Sort with Python and C++ Abhishek Dubey
Trying to learn new things and improve others.

### Solution to the problem.

• Solution in Python
``````import os

def main():
array = []
with open("IntegerArray.txt") as file:
array = [line.strip() for line in file]
mergesort(array)

def merge(a,b):
c = []
count = 0
while len(a) != 0 and len(b) != 0:
if a < b:
c.append(a)
a.remove(a)
count += 1
else:
c.append(b)
b.remove(b)
count += 1
if len(a) == 0:
c += b
else:
c += a
# print("\n\n\n\n"+str(count)+"\n\n\n\n")
return count

def mergesort(x):
if len(x) == 0 or len(x) == 1:
return x
else:
middle = len(x)/2
middle = int(middle)

a = mergesort(x[:middle])
b = mergesort(x[middle:])
return merge(a,b)

if __name__ == '__main__':
main()
``````
• Solution of the same problem in C++.
``````#include "bits/stdc++.h"
#include "iostream"
#include "fstream"
using namespace std;

long long  _mergeSort(long long arr[], long long temp[], long long left, long long right);
long long merge(long long arr[], long long temp[], long long left, long long mid, long long right);

long long mergeSort(long long arr[], long long array_size)
{
long long *temp = (long long *)malloc(sizeof(long long)*array_size);
return _mergeSort(arr, temp, 0, array_size - 1);
}

long long _mergeSort(long long arr[], long long temp[], long long left, long long right)
{
long long mid, inv_count = 0;
if (right > left)
{
mid = (right + left)/2;

inv_count  = _mergeSort(arr, temp, left, mid);
inv_count += _mergeSort(arr, temp, mid+1, right);

inv_count += merge(arr, temp, left, mid+1, right);
}
return inv_count;
}

long long merge(long long arr[], long long temp[], long long left, long long mid, long long right)
{
long long i, j, k;
long long inv_count = 0;

i = left;
j = mid;
k = left;
while ((i <= mid - 1) && (j <= right))
{
if (arr[i] <= arr[j])
{
temp[k++] = arr[i++];
}
else
{
temp[k++] = arr[j++];
inv_count = inv_count + (mid - i);
}
}

while (i <= mid - 1)
temp[k++] = arr[i++];

while (j <= right)
temp[k++] = arr[j++];

for (i=left; i <= right; i++)
arr[i] = temp[i];

return inv_count;
}

int main()
{
long long arr;
ifstream file("..PATH_TO_FILE/file.txt");
if(file.is_open())
{

for(long long i = 0; i < 100000; ++i)
{
file >> arr[i];
}
}

std::cout << mergeSort(arr, 100000);
return 0;
}
``````

## Discussion (1) Sandor Dargo

You have a resource leak in the C++ implementation, you forgot to close the file.

Besides, I'd avoid adding `#include "bits/stdc++.h"` in any code example. It's not portable and it bloats your binary size. Include what you need and know in which header it is.