分区之后枢轴落在哪

以最后一个（23）为枢轴给 [17, 24, 15, 13, 23] 分区。运行下面这段程序：

def partition(a):
    b = list(a)
    pivot = b[-1]
    i = 0
    for j in range(len(b) - 1):
        if b[j] < pivot:
            b[i], b[j] = b[j], b[i]
            i += 1
    b[i], b[-1] = b[-1], b[i]
    return b, i

b, i = partition([17, 24, 15, 13, 23])
print(i)