Count Inversions

import java.util.*;

class Solution {
    // Function to count inversions in the array.
    static int inversionCount(int arr[]) {
        return mergeSort(arr, 0, arr.length - 1);
    }

    private static int mergeSort(int[] arr, int left, int right) {
        int count = 0;
        if (left < right) {
            int mid = left + (right - left) / 2;
            count += mergeSort(arr, left, mid);
            count += mergeSort(arr, mid + 1, right);
            count += merge(arr, mid, left, right);
        }
        return count;
    }

    private static int merge(int[] arr, int mid, int left, int right) {
        int l = left, r = mid + 1;
        int count = 0;
        ArrayList<Integer> temp = new ArrayList<>();
        while (l <= mid && r <= right) {
            if (arr[l] <= arr[r]) {
                temp.add(arr[l]);
                l++;
            } else {
                count += (mid - l + 1);
                temp.add(arr[r]);
                r++;
            }
        }
        while (l <= mid) {
            temp.add(arr[l]);
            l++;
        }
        while (r <= right) {
            temp.add(arr[r]);
            r++;
        }
        for (int i = left; i <= right; i++)
            arr[i] = temp.get(i - left);

        return count;
    }
}