Fenwick 2D

#include <bits/stdc++.h>

struct FenwickTree2D {
    std::vector<std::vector<int>> a;
    int n, m;

    FenwickTree2D(int n, int m)
    : n(n), m(m), a(n, std::vector<int>(m)) {
    }

    void update(int x, int y, int val) {
        int y1;
        while (x < n) {
            y1 = y;
            while (y1 < m) {
                a[x][y1] += val;
                y1 |= y1 + 1;
            }
            x |= x + 1;
        }
    }

    int get(int x, int y) {
        int res = 0;
        int y1;
        while (x >= 0) {
            y1 = y;
            while (y1 >= 0) {
                res += a[x][y1];
                y1 = (y1 & (y1 + 1)) - 1;
            }
            x = (x & (x + 1)) - 1;
        }
        return res;

    }

    int get(int x1, int y1, int x2, int y2) {
        int res = get(x2, y2);
        res -= get(x1 - 1, y2);
        res -= get(x2, y1 - 1);
        res += get(x1 - 1, y1 - 1);
        return res;
    }
};

int main( ) {
    std::ios_base::sync_with_stdio(0);
    std::cin.tie(0);

    int cases;
    std::cin >> cases;
    for (int ti = 0; ti < cases; ++ti) {
        if (ti > 0) {
            std::cout << "\n";
        }

        int n;
        std::cin >> n;
        FenwickTree2D arbol(n + 1, n + 1);

        std::string op;
        std::cin >> op;
        while (op != "END") {

            if (op == "SUM") {
                int x1, y1, x2, y2;
                std::cin >> x1 >> y1 >> x2 >> y2;
                std::cout << arbol.get(x1, y1, x2, y2) << "\n";
            } else if (op == "SET") {
                int x, y, num;
                std::cin >> x >> y >> num;
                arbol.update(x, y, num);
            }
            std::cin >> op;
        }
    }
}