Count Smaller elements

class Solution {
    int[] constructLowerArray(int[] arr) {
        // code here
        int n = arr.length;

        int[] result = new int[n];
        int[] indexes = new int[n];
        for (int i = 0; i < n; i++) {
            indexes[i] = i;
        }
        mergeSort(arr, indexes, result, 0, n - 1);
        return result;
        // code here
    }

    private void mergeSort(int[] arr, int[] indexes, int[] result, int start, int end) {
        if (start >= end) {
            return;
        }
        int mid = start + (end - start) / 2;
        mergeSort(arr, indexes, result, start, mid);
        mergeSort(arr, indexes, result, mid + 1, end);
        merge(arr, indexes, result, start, mid, end);
    }

    private void merge(int[] arr, int[] indexes, int[] result, int start, int mid, int end) {
        int[] tempIndexes = new int[end - start + 1];
        int left = start;
        int right = mid + 1;
        int rightCount = 0;
        int index = 0;
        while (left <= mid && right <= end) {
            if (arr[indexes[right]] < arr[indexes[left]]) {
                tempIndexes[index++] = indexes[right++];
                rightCount++;
            } else {
                tempIndexes[index++] = indexes[left];
                result[indexes[left++]] += rightCount;
            }
        }
        while (left <= mid) {
            tempIndexes[index++] = indexes[left];
            result[indexes[left++]] += rightCount;
        }
        while (right <= end) {
            tempIndexes[index++] = indexes[right++];
        }
        System.arraycopy(tempIndexes, 0, indexes, start, tempIndexes.length);
    }
}