约定输入为正整数行数量，输出如下对称数字金字塔图形：

现有如下C++代码框架，需在第5行横线处填入正确代码：

int lineCount = 0;
cout << "请输入行数量:";
cin >> lineCount;
for (int i = 0; i < lineCount; i++) {
    for (int j = 0; j < ____________; j++) // 此处填写代码
        cout << ' ';
    for (int j = 1; j < i + 1; j++)
        cout << j << " ";
    for (int j = i + 1; j > 0; j--)
        cout << j << " ";
    cout << endl;
}