$O(n)$ 修改，$O(\frac{n}{2})$，然后过去了。

#include <bits/stdc++.h>
using namespace std;
const int N = 1e5 + 5;
#define ll long long
int n, m;
ll a[N];
signed main()
{
    scanf("%d%d", &n, &m);
    while (m --> 0)
    {
        char opt;
        int l, r, v;
        scanf("%1s%d%d", &opt, &l, &r);
        if (opt == 'C')
        {
            scanf("%d", &v);
            for (int i = l; i < r; i++)
                a[i] += v;
        }
        else
        {
            ll ansx = 0, ansy = (ll)(r - l) * (r - l + 1) / 2;
            ll limit = (r - l) >> 1;
            for (int i = l; i < l + limit; i++)
                ansx += (a[i] + a[r - i + l - 1]) * (r - i) * (i - l + 1);
            if ((l + r) & 1)
                ansx += a[(l + r) >> 1] * (limit + 1) * (limit + 1);
            ll gcd = __gcd(ansx, ansy);
            printf("%lld/%lld\n",ansx / gcd, ansy / gcd);
        }
    }
    return 0;
}