2D BIT

int read(int idy, int idx){
    int sum = 0;
    while(idy>0){
        int tmp = idx;
        while(idx>0){
            sum += tree[idy][idx];
            idx -= (idx&-idx);
        }
        idx = tmp;
        idy -= (idy&-idy);
    }
    return sum;
}

void update(int idy, int idx, int val){
    while(idy<=mx){
        int tmp = idx;
        while(idx<=mx){
            tree[idy][idx] += val;
            idx += (idx&-idx);
        }
        idx = tmp;
        idy += (idy&-idy);
    }
}