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CountInversion.c
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CountInversion.c
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#include <stdio.h>
int N; ///Globally declaring the number of elements in the array
int countInv(int arr[], int start, int end) /// A shortcut function to count inversions
{
int count =0;
for(int i=0; i<N; i++)
{
for(int j=i+1; j<N; j++)
{
if(arr[i] > arr[j])
{
count++;
}
}
}
return count;
}
int merge(int arr[], int low, int mid, int high) /// Merging two arrays
{
int temp[N];
int i = low;
int k = low;
int j = mid + 1;
int count = 0;
while((i <= mid) && (j <= high))
{
if(arr[i] <= arr[j])
{
temp[k++] = arr[i++]; //count += ((mid+1)- i); //count as for descending order
}
if(arr[j] <= arr[i])
{
temp[k++] = arr[j++];
count += ((mid+1)- i); //counting for ascending order
}
}
while(i <= mid) temp[k++] = arr[i++];
while(j <= high) temp[k++] = arr[j++];
for(i = low; i <= high; i++)
{
arr[i] = temp[i];
}
return count;
}
int MergeSort(int arr[], int low, int high) ///A function which runs merge sort(a divide and conquer Approach)
{
int mid;
int count = 0;
if(low != high)
{
mid=(low+high)/2;
count += MergeSort(arr, low, mid); //Recursively sending up to mid elements to same function
count += MergeSort(arr, mid+1, high); //Recursively sending up mid+1 to last elements to same function
count += merge(arr, low, mid, high); //Calling merge functions to merge two arrays
}
return count;
}
void main()
{
int n;
printf("Enter the size of the array: ");
scanf("%d", &n); ///Scanning the number of element of the array
N = n;
int arr[n];
printf("Enter the unsorted element: ");
for(int i = 0; i < n; i++) ///Scanning the elements of the array
scanf("%d", &arr[i]);
int count = MergeSort(arr, 0, n-1); ///MergeSort is a function which runs merge sort(a divide and conquer Approach)
printf("\nPrinting the sorted array: "); ///Printing the array in ascending order
for(int i = 0; i < n; i++)
printf("%d ", arr[i]);
printf("\nThe count inversion : %d", count); ///Printing the number of Count Inversions
}