Count inversion in an array, O(nlogn) approach

import java.util.*;

public class Main {

    private static int merge(int[] arr, int low, int mid, int high) {

        ArrayList<Integer> temp = new ArrayList<>(); // temporary array

        int left = low;      // starting index of left half of arr

        int right = mid + 1;   // starting index of right half of arr

        //Modification 1: cnt variable to count the pairs:

        int cnt = 0;

        //storing elements in the temporary array in a sorted manner//

        while (left <= mid && right <= high) {

            if (arr[left] <= arr[right]) {

                temp.add(arr[left]);

                left++;

            } else {

                temp.add(arr[right]);

                cnt += (mid - left + 1); //Modification 2

                right++;

            }

        }

        // if elements on the left half are still left //

        while (left <= mid) {

            temp.add(arr[left]);

            left++;

        }

        //  if elements on the right half are still left //

        while (right <= high) {

            temp.add(arr[right]);

            right++;

        }

        // transfering all elements from temporary to arr //

        for (int i = low; i <= high; i++) {

            arr[i] = temp.get(i - low);

        }

        return cnt; // Modification 3

    }

    public static int mergeSort(int[] arr, int low, int high) {

        int cnt = 0;

        if (low >= high) return cnt;

        int mid = (low + high) / 2 ;

        cnt += mergeSort(arr, low, mid);  // left half

        cnt += mergeSort(arr, mid + 1, high); // right half

        cnt += merge(arr, low, mid, high);  // merging sorted halves

        return cnt;

    }

    public static int numberOfInversions(int[] a, int n) {

        // Count the number of pairs:

        return mergeSort(a, 0, n - 1);

    }

    public static void main(String[] args) {

        //int[] a = {5, 4, 3, 2, 1};

        //int n = 5;

        int[] a = {1,3,5,2,4,6};

        int n = 6;

        int cnt = numberOfInversions(a, n);

        System.out.println("The number of inversions are: " + cnt);

    }

}