Merge sort

def sl(left, right):
    i = j = 0
    res = []
    while i < len(left) and j < len(right):
        if left[i] < right[j]:
            res.append(left[i])
            i += 1
        else:
            res.append(right[j])
            j += 1

    if i < len(left):
        for index in range(i, len(left)):
            res.append(left[index])
    else:
        for index in range(j, len(right)):
            res.append(right[index])
    print(f"arr is {res}")
    return res


# 5, 4
# 5
def merge(arr):
    if len(arr) < 2:
        return arr
    else:
        index = len(arr) // 2
        left = merge(arr[:index]) # [3]
        right = merge(arr[index:]) # [3, 4, 5]
        return sl(left, right) # [4, 5]

arr = [5, 4, 3, 2, 1]
print(merge(arr))