一个“简单”的整数问题

#define _CRT_SECURE_NO_WARNINGS 1
#include <bits/stdc++.h>

using namespace std;
//#define int long long
//#define map unordered_map
typedef long long ll;
const int N = 1e5 + 10, M = 350;
int n, m;
int a[N];
ll sum[M], add[M];
int len;

int get(int i)
{
    return i / len;
}

ll ask(int l, int r)
{
    ll res = 0;
    int L = get(l), R = get(r);
    if (L == R)
    {
        for (int i = l; i <= r; ++i)
        {
            int I = get(i);
            res += (a[i] + add[I]);
        }
    }
    else
    {
        int i = l, j = r, I, J;
        while ((I = get(i)) == L) {
            res += (a[i] + add[I]), ++i;
        }
        while ((J = get(j)) == R) {
            res += (a[j] + add[J]), --j;
        }
        for (int k = I; k <= J; ++k) {
            res += sum[k];
        }
    }
    return res;
}

void modify(int l, int r, int d)
{
    int L = get(l), R = get(r);
    if (L == R)
    {
        for (int i = l; i <= r; ++i)
        {
            int I = get(i);
            a[i] += d, sum[I] += d;
        }
    }
    else
    {
        int i = l, j = r, I, J;
        while ((I = get(i)) == L) {
            a[i] += d, sum[I] += d, ++i;
        }
        while ((J = get(j)) == R) {
            a[j] += d, sum[J] += d, --j;
        }
        for (int k = I; k <= J; ++k){
            sum[k] += (len * d), add[k] += d;
        }
    }
}

signed main()
{
    cin >> n >> m;
    len = n / sqrt(n);
    for (int i = 1; i <= n; ++i)
    {
        int I = get(i);
        scanf("%d", &a[i]);
        sum[I] += a[i];
    }

    while (m--)
    {
        char op[2]; int l, r, d;
        scanf("%s%d%d", op, &l, &r);
        if (*op == 'Q')
        {
            printf("%lld\n", ask(l, r));
        }
        else
        {
            scanf("%d", &d);
            modify(l, r, d);
        }
    }

    return 0;
}