def partition(arr, low, high):
    pivot = arr[low]
    i = low
    j = high
    while i < j:
        while i < j and arr[j] >= pivot:
            j -= 1
        while i < j and arr[i] <= pivot:
            i += 1
        if i < j:
            arr[i], arr[j] = arr[j], arr[i]
    ________________ # 在此处填入代码
    return i