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C Program/inversion_count.cpp

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+#include <bits/stdc++.h>
+using namespace std;
+int merge(int arr[], int low, int mid, int high)
+{
+ int i = low, j = mid + 1, k = low;
+ int b[high];
+ int count=0;
+ while (i <= mid && j <= high)
+ {
+ if (arr[i] <= arr[j])
+ {
+ b[k] = arr[i];
+ i++;
+ k++;
+ }
+ else
+ {
+ b[k] = arr[j];
+ j++;
+ k++;
+ count+=mid+1-i;
+ }
+ }
+ if (i > mid)
+ {
+ while (j<=high)
+ {
+ b[k]=arr[j];
+ j++;
+ k++;
+ }
+
+ }
+ else{
+ while (i<=mid)
+ {
+ b[k]=arr[i];
+ i++;
+ k++;
+ }
+
+ }
+ for(k=low;k<=high;k++)
+ arr[k]=b[k];
+
+ return count;
+}
+int mergesort(int arr[], int low, int high)
+{
+ int mid;
+ int count = 0;
+ if (high > low)
+ {
+ mid = (high + low) / 2;
+ count += mergesort(arr, low, mid);
+ count += mergesort(arr, mid + 1, high);
+ count += merge(arr, low, mid, high);
+ }
+
+ return count;
+}
+int main()
+{
+
+ int n;
+ cout << "enter array length=";
+ cin >> n;
+ int arr[n];
+ cout << "\n enter array to be sorted=";
+ for (int i = 0; i < n; i++)
+ {
+ cin >> arr[i];
+ }
+
+ cout << mergesort(arr, 0, n);
+ cout << endl;
+return 0;
+}