计算合并排序中的交换数量(Java)

public class MergeSort {
    private static int swapCount = 0;

    public static void mergeSort(int[] arr) {
        if (arr == null || arr.length <= 1) {
            return;
        }
        mergeSort(arr, 0, arr.length - 1);
    }

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

    private static void merge(int[] arr, int start, int mid, int end) {
        int[] temp = new int[end - start + 1];
        int i = start, j = mid + 1, k = 0;
        while (i <= mid && j <= end) {
            if (arr[i] <= arr[j]) {
                temp[k++] = arr[i++];
            } else {
                temp[k++] = arr[j++];
                swapCount++; // 进行交换操作，交换数量加1
            }
        }
        while (i <= mid) {
            temp[k++] = arr[i++];
        }
        while (j <= end) {
            temp[k++] = arr[j++];
        }
        System.arraycopy(temp, 0, arr, start, temp.length);
    }

    public static void main(String[] args) {
        int[] arr = {5, 2, 8, 4, 1};
        mergeSort(arr);
        System.out.println("交换数量：" + swapCount);
    }
}