标准做法

# include <iostream>
using namespace std;
const int N = 1e5 + 10;
int m, n, x, q[N];
int main()
{
    scanf("%d%d", &n, &m);
    for (int i = 0; i < n; i ++) scanf("%d", &q[i]);
    while ( m-- )
    {
        scanf("%d", &x);

        int l = 0, r = n - 1;
        while (l < r)
        {
            int mid = l + r >> 1;
            if (q[mid] >= x) r = mid;
            else l = mid + 1;
        }
        if (q[l] != x) printf("-1 -1\n");
        else
        {
            printf("%d ", l);
            // while (q[l + 1] == x) l ++;
            int l = 0, r = n - 1;
            while (l < r)
            {
                int mid = l + r + 1 >> 1;
                if (q[mid] <= x) l = mid;
                else r = mid - 1;
            }

            printf("%d\n", l);
        }
    }
    return 0;

}

投机取巧

# include <iostream>
using namespace std;
const int N = 1e5 + 10;
int m, n, x, q[N];
int main()
{
    scanf("%d%d", &n, &m);
    for (int i = 0; i < n; i ++) scanf("%d", &q[i]);
    while ( m-- )
    {
        scanf("%d", &x);

        int l = 0, r = n - 1;
        while (l < r)
        {
            int mid = l + r >> 1;
            if (q[mid] >= x) r = mid;
            else l = mid + 1;
        }
        if (q[l] != x) printf("-1 -1\n");
        else
        {
            printf("%d ", l);
            while (q[l + 1] == x) l ++;
            printf("%d\n", l);
        }
    }
    return 0;

}