有 n 位同学的成绩已经从小到大排好序，现在对它执行下面这段以第一个元素为 pivot 的快速排序，请问此次排序的时间复杂度是（）。

def quicksort(a, l, r):
    if l >= r:
        return
    pivot = a[l]
    i, j = l, r

    while i < j:
        while i < j and a[j] >= pivot:
            j -= 1
        while i < j and a[i] <= pivot:
            i += 1
        if i < j:
            a[i], a[j] = a[j], a[i]

    a[l], a[i] = a[i], a[l]

    quicksort(a, l, i - 1)
    quicksort(a, i + 1, r)

if __name__ == "__main__":
    scores = [60, 70, 80, 90, 100]
    print("排序前：", scores)
    quicksort(scores, 0, len(scores)-1)
    print("排序后：", scores) # 输出：[60, 70, 80, 90, 100]
    def quicksort_with_log(a, l, r, depth=0):
        if l >= r:
            return
        print(f"递归深度{depth}，处理区间[{l},{r}]，数组：{a[l:r+1]}")
        pivot = a[l]
        i, j = l, r
        while i < j:
            while i < j and a[j] >= pivot: j -= 1
            while i < j and a[i] <= pivot: i += 1
            if i < j: a[i], a[j] = a[j], a[i]
        a[l], a[i] = a[i], a[l]
        quicksort_with_log(a, l, i-1, depth+1)
        quicksort_with_log(a, i+1, r, depth+1)

    scores2 = [60,70,80,90,100]
    print("\n递归过程：")
    quicksort_with_log(scores2, 0, 4)

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