请求解释归并排序算法Merge步骤的伪代码逻辑

您好，我有一个问题希望得到帮助。我理解归并排序算法Merge步骤的工作原理，但完全看不懂其伪代码。我已经实现了这段代码，但仍不理解它的逻辑，恳请有人为我解释，谢谢。

归并排序伪代码 #

MERGE-SORT(A, p, r)
    if p < r
        q = floor((p + r)/2)
        MERGE-SORT(A, p, q)
        MERGE-SORT(A, q+1, r)
        MERGE(A, p, q, r)

Merge步骤伪代码 #

MERGE(A, p, q, r)
    n1 = q - p + 1
    n2 = r - q
    let L[1..n1+1] and R[1..n2+1] be new arrays
    for i = 1 to n1
        L[i] = A[p + i - 1]
    for j = 1 to n2
        R[j] = A[q + j]
    L[n1+1] = ∞
    R[n2+1] = ∞
    i = 1
    j = 1
    for k = p to r
        if L[i] ≤ R[j]
            A[k] = L[i]
            i = i + 1
        else
            A[k] = R[j]
            j = j + 1

内容的提问来源于stack exchange，提问作者luna_98