在归并排序的合并操作中，如下代码片段可以正确地将两个已排序的子数组 L 和 R 合并回原数组 arr 中。

def merge(arr, left, mid, right):
    n1 = mid - left + 1
    n2 = right - mid
    L = [0] * n1
    R = [0] * n2

    for i in range(n1):
        L[i] = arr[left + i]
    for j in range(n2):
        R[j] = arr[mid + 1 + j]

    i = 0
    j = 0
    k = left

    while i < n1 and j < n2:
        if L[i] <= R[j]:
            arr[k] = L[i]
            i += 1
        else:
            arr[k] = R[j]
            j += 1
        k += 1

    while i < n1:
        arr[k] = L[i]
        i += 1
        k += 1

    while j < n2:
        arr[k] = R[j]
        j += 1
        k += 1