int partition(vector<int>& arr, int low, int high) {
    int pivot = arr[high]; // 基准值
    int i = low - 1;

    for (int j = low; j < high; j++) {
        ________________________________ // 在此处填入代码
    }
    swap(arr[i + 1], arr[high]);
    return i + 1;
}

// 快速排序
void quickSort(vector<int>& arr, int low, int high) {
    if (low < high) {
        int pi = partition(arr, low, high);
        quickSort(arr, low, pi - 1);
        quickSort(arr, pi + 1, high);
    }
}