排序算法-归并排序

def merge(arrA, arrB):
    arr = []
    i,j = 0,0
    while i < len(arrA) and j < len(arrB):
        if arrA[i] < arrB[j]:
            arr.append(arrA[i])
            i+=1
        else:
            arr.append(arrB[j])
            j+=1
    
    for start in range(i, len(arrA)):
        arr.append(arrA[start])
    
    for start in range(j, len(arrB)):
        arr.append(arrB[start])
    return arr


def merge_sort(arr):
    if len(arr) <= 1:
        return
    mid = len(arr) // 2
    arrA = merge_sort(arr[:mid])
    arrB = merge_sort(arr[mid:])
    return merge(arrA, arrB)