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

    for (int j = left; j < right; j++) {
        if (arr[j] < pivot) {
            i++;
            swap(arr[i], arr[j]);
        }
    }
    swap(arr[i + 1], arr[right]);
    return i + 1;
}

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