Присвоение на отрезке и сумма на отрезке

#include <bits/stdc++.h>
#define ll long long

using namespace std;

ll n, k, q;
vector<ll> a, b, add;

void push(int id) {
    if (add[id] != -1) {
        b[id] = 0;
        for (int i = id * k; i < min((id + 1) * k, n); ++i) {
            a[i] = add[id];
            b[id] += a[i];
        }
        add[id] = -1;
    }
}

void update(int l, int r, ll x) {
    int bl = l / k, br = r / k;
    if (bl != br) {
        push(bl);
        push(br);

        for (int i = l; i < (bl + 1) * k; i++) {
            b[bl] -= a[i];
            a[i] = x;
            b[bl] += a[i];
        }
        for (int i = br * k; i <= r; ++i) {
            b[br] -= a[i];
            a[i] = x;
            b[br] += a[i];
        }
        for (int i = bl + 1; i < br; ++i) {
            b[i] = k * x;
            add[i] = x;
        }
    } else {
        push(bl);

        for (int i = l; i <= r; ++i) {
            b[i / k] -= a[i];
            a[i] = x;
            b[i / k] += a[i];
        }
    }
}

ll sum(int l, int r) {
    int bl = l / k, br = r / k;

    ll res = 0;

    if (bl != br) {
        push(bl);
        push(br);

        for (int i = l; i < (bl + 1) * k; ++i) {
            res += a[i];
        }
        for (int i = br * k; i <= r; ++i) {
            res += a[i];
        }
        for (int i = bl + 1; i < br; ++i) {
            res += b[i];
        }
    } else {
        push(bl);

        for (int i = l; i <= r; ++i) {
            res += a[i];
        }
    }

    return res;
}

int main() {
    freopen("sum.in", "r", stdin);
    freopen("sum.out", "w", stdout);
    cin >> n >> q;
    a.resize(n);
    k = int(sqrt(n) + 0.99);
    b.resize(k + 1, 0);
    add.resize(k + 1, -1);

    while (q--) {
        char op;
        int l, r;
        cin >> op >> l >> r;
        l--; r--;
        if (op == 'A') {
            int x;
            cin >> x;
            update(l, r, x);
        } else {
            cout << sum(l, r) << endl;
        }
    }

    return 0;
}