二维树状数组模板

void add(int x, int y, int d) {    int i, j;    for(i = x; i < N; i += lowbit(i))        for(j = y; j < N; j += lowbit(j))            mat[i][j] += d;}LL sum(int x, int y) {    LL res = 0;    int i, j;    for(i = x; i > 0; i -= lowbit(i))        for(j = y; j > 0; j -= lowbit(j))            res += mat[i][j];    return res;}