树状数组写法

树状数组写法

标准写法

template <int N>
struct fenwick {
  int t[N + 1];
  void add(int x, int k) {
    for (; x <= N; x += x & -x) t[x] += k;
  }
  int query(int x, int r = 0) {
    for (; x >= 1; x -= x & -x) r += t[x];
    return r;
  }
};

查询后缀和

template <int N>
struct fenwick {
  int t[N + 1];
  void add(int x, int k) {
    for (; x >= 1; x -= x & -x) t[x] += k;
  }
  int query(int x, int r = 0) {
    for (; x <= N; x += x & -x) r += t[x];
    return r;
  }
};

0-indexed

template <int N>
struct fenwick {
  int t[N];
  void add(int x, int k) {
    for (; x < N; x |= x + 1) t[x] += k;
  }
  int query(int x, int r = 0) { // [0, x)
    for (; x--; x &= x + 1) r += t[x];
    return r;
  }
};