BIT 1D, BIT 2D

// Đây là code BIT 1D
=====================

const int N=100005;
int T[N];

void update(int u, int x){
   for (int i=u; i<N; i+=i&-i)
   T[i]+=x;
}

int get(int u, int x){
   int Sum = 0;
   for (int i=u; i>0; i-=i&-i)
   Sum += T[i];
   return Sum;
}

// Đây là code BIT 1D anh dùng
==============================

struct fenwick_tree{
   int T[N];
   void update(int u, int x)
      { for (int i=u; i<N; i+=i&-i) T[i]+=x; }
   int get(int u)
      { int Sum=T[u]; while (u-=u&-u) Sum+=T[u]; return Sum; }
} BIT;

// Đây là code BIT 2D
=====================

void update(int x, int y, int k){
   for (int i=x; i<N; i+=i&-i)
   for (int j=y; j<N; j+=j&-j)
   T[i][j]+=k;
}

int get(int x, int y){
   int Sum = 0;
   for (int i=x; i>0; i-=i&-i)
   for (int j=y; j>0; j-=j&-j)
   Sum += T[i][j];
   return Sum;
}