二、阅读程序（判断题每题1分，选择题每题3分，共计40分；判断题正确填 T，错误填 F）

第1题

int solve(int n, int a[], int b[])
{
    std::sort(a, a + n);
    std::sort(b, b + n);

    int ans = std::abs(a[0] - b[0]);
    int i = 0, j = 0;

    while (i < n && j < n)
    {
        if (a[i] < b[j])
        {
            int diff = b[j] - a[i];
            if (ans > diff)
                ans = diff;
            i++;
        }
        else
        {
            int diff = a[i] - b[j];
            if (ans > diff)
                ans = diff;
            j++;
        }
    }
    return ans;
}

当 $n=3$，a=[5,1,12]，b=[7,9,4] 时，程序返回（ ）。

{{ select(1) }}

• $1$
• $2$
• $3$
• $4$