歸並排序

def merge_sort(arr):
    length = len(arr)
    if length <= 1:
        return arr
    mid = length // 2
    left = merge_sort(arr[mid:])
    right = merge_sort(arr[:mid])

    return merge(left, right)


def merge(arr1, arr2):
    l, r = 0, 0
    res = []
    while l < len(arr1) and r < len(arr2):
        if arr1[l] > arr2[r]:
            res.append(arr2[r])
            r += 1
        else:
            res.append(arr1[l])
            l += 1
    res += arr1[l:]
    res += arr2[r:]
    return res


if __name__ == '__main__':
    l = [5, 9, 1, 11, 6, 7, 2, 4]
    print(merge_sort(l))