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:heavy_check_mark: ds/segtree/sortable_segtree.hpp

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Code

#include "ds/fastset.hpp"
#include "ds/segtree/segtree.hpp"
#include "ds/node_pool.hpp"

template <typename Monoid>
struct Sortable_SegTree {
  using MX = Monoid;
  using X = typename MX::value_type;
  const int N, KEY_MAX;

  struct Node {
    X x, rev_x;
    int size;
    Node *l, *r;
  };
  Node_Pool<Node> pool;
  using np = Node*;

  FastSet ss;       // 区間の左端全体を表す fastset
  SegTree<MX> seg;  // 区間を集約した値を区間の左端にのせた segtree
  vector<np> root;  // 区間の左端に、dynamic segtree の node を乗せる
  vector<bool> rev;

  Sortable_SegTree(int KEY_MAX, vector<int> key, vector<X> dat)
      : N(key.size()), KEY_MAX(KEY_MAX), ss(key.size()), seg(dat) {
    init(key, dat);
  }
  void set(int i, int key, const X& x) {
    assert(key < KEY_MAX);
    split_at(i), split_at(i + 1);
    rev[i] = 0, root[i] = new_node();
    set_rec(root[i], 0, KEY_MAX, key, x);
    seg.set(i, x);
  }

  X prod_all() { return seg.prod_all(); }

  X prod(int l, int r) {
    split_at(l), split_at(r);
    return seg.prod(l, r);
  }

  void sort_inc(int l, int r) {
    split_at(l), split_at(r);
    while (1) {
      np c = root[l];
      int i = ss.next(l + 1);
      if (i == r) break;
      root[l] = merge(c, root[i]);
      ss.erase(i), seg.set(i, MX::id());
    }
    rev[l] = 0, seg.set(l, root[l]->x);
  };

  void sort_dec(int l, int r) {
    sort_inc(l, r), rev[l] = 1;
    seg.set(l, root[l]->rev_x);
  };

  pair<vc<int>, vc<X>> get_all() {
    vector<int> key;
    vector<X> dat;
    key.reserve(N);
    dat.reserve(N);
    auto dfs = [&](auto& dfs, np n, int l, int r, bool rev) -> void {
      if (!n) return;
      if (r == l + 1) {
        key.eb(l), dat.eb(n->x);
        return;
      }
      int m = (l + r) / 2;
      if (!rev) {
        dfs(dfs, n->l, l, m, rev), dfs(dfs, n->r, m, r, rev);
      }
      if (rev) {
        dfs(dfs, n->r, m, r, rev), dfs(dfs, n->l, l, m, rev);
      }
    };
    for (int i = 0; i < N; ++i) {
      if (ss[i]) dfs(dfs, root[i], 0, KEY_MAX, rev[i]);
    }
    return {key, dat};
  }

 private:
  void init(vector<int>& key, vector<X>& dat) {
    rev.assign(N, 0), root.clear(), root.reserve(N);
    seg.build(N, [&](int i) -> X { return dat[i]; });
    for (int i = 0; i < N; ++i) {
      ss.insert(i);
      root.eb(new_node(MX::id()));
      assert(key[i] < KEY_MAX);
      set_rec(root[i], 0, KEY_MAX, key[i], dat[i]);
    }
  }

  // x が左端になるようにする
  void split_at(int x) {
    if (x == N || ss[x]) return;
    int a = ss.prev(x), b = ss.next(a + 1);
    ss.insert(x);
    if (!rev[a]) {
      auto [nl, nr] = split(root[a], x - a);
      root[a] = nl, root[x] = nr;
      rev[a] = rev[x] = 0;
      seg.set(a, root[a]->x), seg.set(x, root[x]->x);
    } else {
      auto [nl, nr] = split(root[a], b - x);
      root[a] = nr, root[x] = nl;
      rev[a] = rev[x] = 1;
      seg.set(a, root[a]->rev_x), seg.set(x, root[x]->rev_x);
    }
  }

  void rebuild() {
    auto [key, dat] = get_all();
    pool.reset();
    init(key, dat);
  }

  np new_node(X x = MX::id()) {
    np c = pool.create();
    c->x = c->rev_x = x;
    c->l = c->r = nullptr;
    c->size = 1;
    return c;
  }

  pair<np, np> split(np n, int k) {
    if (k == 0) {
      return {nullptr, n};
    }
    if (k == n->size) {
      return {n, nullptr};
    }
    int s = (n->l ? n->l->size : 0);
    Node* b = new_node();
    if (k <= s) {
      auto [nl, nr] = split(n->l, k);
      b->l = nr, b->r = n->r, n->l = nl, n->r = nullptr;
    }
    if (k > s) {
      auto [nl, nr] = split(n->r, k - s);
      n->l = n->l, n->r = nl, b->l = nullptr, b->r = nr;
    }
    update(n), update(b);
    return {n, b};
  }

  np merge(np a, np b) {
    if (!a) return b;
    if (!b) return a;
    a->l = merge(a->l, b->l), a->r = merge(a->r, b->r);
    update(a);
    return a;
  }

  void update(np n) {
    if (!(n->l) && !(n->r)) {
      return;
    }
    if (!(n->l)) {
      n->x = n->r->x, n->rev_x = n->r->rev_x, n->size = n->r->size;
      return;
    }
    if (!(n->r)) {
      n->x = n->l->x, n->rev_x = n->l->rev_x, n->size = n->l->size;
      return;
    }
    n->x = MX::op(n->l->x, n->r->x);
    n->rev_x = MX::op(n->r->rev_x, n->l->rev_x);
    n->size = n->l->size + n->r->size;
  }

  void set_rec(np n, int l, int r, int k, const X& x) {
    if (r == l + 1) {
      n->x = n->rev_x = x;
      return;
    }
    int m = (l + r) / 2;
    if (k < m) {
      if (!(n->l)) n->l = new_node();
      set_rec(n->l, l, m, k, x);
    }
    if (m <= k) {
      if (!(n->r)) n->r = new_node();
      set_rec(n->r, m, r, k, x);
    }
    update(n);
  }
};
#line 1 "other/bit.hpp"

int popcnt(int x) { return __builtin_popcount(x); }
int popcnt(u32 x) { return __builtin_popcount(x); }
int popcnt(ll x) { return __builtin_popcountll(x); }
int popcnt(u64 x) { return __builtin_popcountll(x); }
int popcnt_sgn(int x) { return (__builtin_parity(unsigned(x)) & 1 ? -1 : 1); }
int popcnt_sgn(u32 x) { return (__builtin_parity(x) & 1 ? -1 : 1); }
int popcnt_sgn(ll x) { return (__builtin_parityll(x) & 1 ? -1 : 1); }
int popcnt_sgn(u64 x) { return (__builtin_parityll(x) & 1 ? -1 : 1); }
// (0, 1, 2, 3, 4) -> (-1, 0, 1, 1, 2)
int topbit(int x) { return (x == 0 ? -1 : 31 - __builtin_clz(x)); }
int topbit(u32 x) { return (x == 0 ? -1 : 31 - __builtin_clz(x)); }
int topbit(ll x) { return (x == 0 ? -1 : 63 - __builtin_clzll(x)); }
int topbit(u64 x) { return (x == 0 ? -1 : 63 - __builtin_clzll(x)); }
// (0, 1, 2, 3, 4) -> (-1, 0, 1, 0, 2)
int lowbit(int x) { return (x == 0 ? -1 : __builtin_ctz(x)); }
int lowbit(u32 x) { return (x == 0 ? -1 : __builtin_ctz(x)); }
int lowbit(ll x) { return (x == 0 ? -1 : __builtin_ctzll(x)); }
int lowbit(u64 x) { return (x == 0 ? -1 : __builtin_ctzll(x)); }

template <typename T>
T kth_bit(int k) {
  assert(0 <= k && k < int(8 * sizeof(T)));
  return T(1) << k;
}
template <typename T>
bool has_kth_bit(T x, int k) {
  assert(0 <= k && k < int(8 * sizeof(T)));
  return x >> k & 1;
}

template <typename UINT>
struct all_bit {
  static_assert(is_unsigned<UINT>::value);
  UINT s;
  all_bit(UINT s) : s(s) {}
  struct iter {
    UINT s;
    int operator*() const { return lowbit(s); }
    void operator++() { s &= s - 1; }
    bool operator!=(nullptr_t) const { return s; }
  };
  iter begin() const { return {s}; }
  nullptr_t end() const { return nullptr; }
};

template <typename UINT>
struct all_subset {
  static_assert(is_unsigned<UINT>::value);
  UINT s;
  all_subset(UINT s) : s(s) {}
  struct iter {
    UINT s, t;
    bool done = false;
    UINT operator*() const { return t; }
    void operator++() {
      done = (t == 0);
      t = (t - 1) & s;
    }
    bool operator!=(nullptr_t) const { return !done; }
  };
  iter begin() const { return {s, s}; }
  nullptr_t end() const { return nullptr; }
};

constexpr u64 full_mask(int n) {
  assert(0 <= n && n <= 64);
  return n == 64 ? -1ULL : (1ULL << n) - 1;
}

u64 bit_reverse(u64 x) {
  x = ((x & 0x5555555555555555ULL) << 1) | ((x >> 1) & 0x5555555555555555ULL);
  x = ((x & 0x3333333333333333ULL) << 2) | ((x >> 2) & 0x3333333333333333ULL);
  x = ((x & 0x0f0f0f0f0f0f0f0fULL) << 4) | ((x >> 4) & 0x0f0f0f0f0f0f0f0fULL);
  x = ((x & 0x00ff00ff00ff00ffULL) << 8) | ((x >> 8) & 0x00ff00ff00ff00ffULL);
  x = ((x & 0x0000ffff0000ffffULL) << 16) | ((x >> 16) & 0x0000ffff0000ffffULL);
  x = (x << 32) | (x >> 32);
  return x;
}
#line 2 "ds/fastset.hpp"

// 64-ary tree
// space: (N/63) * u64
struct FastSet {
  static constexpr u32 B = 64;
  int n = 0, log = 0;
  vvc<u64> seg;

  FastSet() {}
  FastSet(int n) { build(n); }

  int size() { return n; }

  void fill_one() {
    int cur = n;
    for (auto& vs : seg) {
      int p = cur / B, q = cur % B;
      FOR(i, p) vs[i] = -1ull;
      if (q) vs[p] = full_mask(q);
      cur = (cur + B - 1) / B;
    }
  }

  template <typename F>
  FastSet(int n, F f) {
    build(n, f);
  }

  void build(int m) {
    seg.clear();
    n = m;
    do {
      seg.push_back(vc<u64>((m + B - 1) / B));
      m = (m + B - 1) / B;
    } while (m > 1);
    log = len(seg);
  }
  template <typename F>
  void build(int n, F f) {
    build(n);
    FOR(i, n) { seg[0][i / B] |= u64(bool(f(i))) << (i % B); }
    FOR(h, log - 1) {
      FOR(i, len(seg[h])) {
        seg[h + 1][i / B] |= u64(bool(seg[h][i])) << (i % B);
      }
    }
  }

  bool operator[](int i) const {
    assert(0 <= i && i < n);
    return seg[0][i / B] >> (i % B) & 1;
  }
  void insert(int i) {
    assert(0 <= i && i < n);
    for (int h = 0; h < log; h++) {
      seg[h][i / B] |= u64(1) << (i % B), i /= B;
    }
  }
  void add(int i) { insert(i); }
  void erase(int i) {
    assert(0 <= i && i < n);
    u64 x = 0;
    for (int h = 0; h < log; h++) {
      seg[h][i / B] &= ~(u64(1) << (i % B));
      seg[h][i / B] |= x << (i % B);
      x = bool(seg[h][i / B]);
      i /= B;
    }
  }
  void remove(int i) { erase(i); }

  // min[x,n) or n
  int next(int i) {
    assert(i <= n);
    chmax(i, 0);
    for (int h = 0; h < log; h++) {
      if (i / B == seg[h].size()) break;
      u64 d = seg[h][i / B] >> (i % B);
      if (!d) {
        i = i / B + 1;
        continue;
      }
      i += lowbit(d);
      for (int g = h - 1; g >= 0; g--) {
        i *= B;
        i += lowbit(seg[g][i / B]);
      }
      return i;
    }
    return n;
  }

  // max [0,x], or -1
  int prev(int i) {
    assert(i >= -1);
    if (i >= n) i = n - 1;
    for (int h = 0; h < log; h++) {
      if (i == -1) break;
      u64 d = seg[h][i / B] << (63 - i % B);
      if (!d) {
        i = i / B - 1;
        continue;
      }
      i -= __builtin_clzll(d);
      for (int g = h - 1; g >= 0; g--) {
        i *= B;
        i += topbit(seg[g][i / B]);
      }
      return i;
    }
    return -1;
  }

  bool any(int l, int r) {
    assert(0 <= l && l <= r && r <= n);
    return next(l) < r;
  }

  // [l, r)
  template <typename F>
  void enumerate(int l, int r, F f) {
    assert(0 <= l && l <= r && r <= n);
    for (int x = next(l); x < r; x = next(x + 1)) f(x);
  }

  void reset() {
    enumerate(0, n, [&](int i) -> void { erase(i); });
  }

  string to_string() {
    string s(n, '?');
    for (int i = 0; i < n; ++i) s[i] = ((*this)[i] ? '1' : '0');
    return s;
  }
};
#line 1 "ds/segtree/segtree.hpp"

template <class Monoid>
struct SegTree {
  using MX = Monoid;
  using X = typename MX::value_type;
  using value_type = X;
  vc<X> dat;
  int n, log, size;

  SegTree() {}
  SegTree(int n) { build(n); }
  template <typename F>
  SegTree(int n, F f) {
    build(n, f);
  }
  SegTree(const vc<X>& v) { build(v); }

  void build(int m) {
    build(m, [](int i) -> X { return MX::id(); });
  }
  void build(const vc<X>& v) {
    build(len(v), [&](int i) -> X { return v[i]; });
  }
  template <typename F>
  void build(int m, F f) {
    n = m, log = 1;
    while ((1 << log) < n) ++log;
    size = 1 << log;
    dat.assign(size << 1, MX::id());
    FOR(i, n) dat[size + i] = f(i);
    FOR_R(i, 1, size) update(i);
  }

  X get(int i) const { return dat[size + i]; }
  vc<X> get_all() const { return {dat.begin() + size, dat.begin() + size + n}; }

  void update(int i) { dat[i] = Monoid::op(dat[2 * i], dat[2 * i + 1]); }
  void set(int i, const X& x) {
    assert(i < n);
    dat[i += size] = x;
    while (i >>= 1) update(i);
  }

  void multiply(int i, const X& x) {
    assert(i < n);
    i += size;
    dat[i] = Monoid::op(dat[i], x);
    while (i >>= 1) update(i);
  }

  X prod(int L, int R) const {
    assert(0 <= L && L <= R && R <= n);
    X vl = Monoid::id(), vr = Monoid::id();
    L += size, R += size;
    while (L < R) {
      if (L & 1) vl = Monoid::op(vl, dat[L++]);
      if (R & 1) vr = Monoid::op(dat[--R], vr);
      L >>= 1, R >>= 1;
    }
    return Monoid::op(vl, vr);
  }

  vc<int> prod_ids(int L, int R) const {
    assert(0 <= L && L <= R && R <= n);
    vc<int> I, J;
    L += size, R += size;
    while (L < R) {
      if (L & 1) I.eb(L++);
      if (R & 1) J.eb(--R);
      L >>= 1, R >>= 1;
    }
    reverse(all(J));
    concat(I, J);
    return I;
  }

  X prod_all() const { return dat[1]; }

  template <class F>
  int max_right(F check, int L) const {
    assert(0 <= L && L <= n && check(Monoid::id()));
    if (L == n) return n;
    L += size;
    X sm = Monoid::id();
    do {
      while (L % 2 == 0) L >>= 1;
      if (!check(Monoid::op(sm, dat[L]))) {
        while (L < size) {
          L = 2 * L;
          if (check(Monoid::op(sm, dat[L]))) {
            sm = Monoid::op(sm, dat[L++]);
          }
        }
        return L - size;
      }
      sm = Monoid::op(sm, dat[L++]);
    } while ((L & -L) != L);
    return n;
  }

  template <class F>
  int min_left(F check, int R) const {
    assert(0 <= R && R <= n && check(Monoid::id()));
    if (R == 0) return 0;
    R += size;
    X sm = Monoid::id();
    do {
      --R;
      while (R > 1 && (R % 2)) R >>= 1;
      if (!check(Monoid::op(dat[R], sm))) {
        while (R < size) {
          R = 2 * R + 1;
          if (check(Monoid::op(dat[R], sm))) {
            sm = Monoid::op(dat[R--], sm);
          }
        }
        return R + 1 - size;
      }
      sm = Monoid::op(dat[R], sm);
    } while ((R & -R) != R);
    return 0;
  }

  // prod_{l<=i<r} A[i xor x]
  X xor_prod(int l, int r, int xor_val) const {
    static_assert(Monoid::commute);
    X x = Monoid::id();
    for (int k = 0; k < log + 1; ++k) {
      if (l >= r) break;
      if (l & 1) {
        x = Monoid::op(x, dat[(size >> k) + ((l++) ^ xor_val)]);
      }
      if (r & 1) {
        x = Monoid::op(x, dat[(size >> k) + ((--r) ^ xor_val)]);
      }
      l /= 2, r /= 2, xor_val /= 2;
    }
    return x;
  }
};
#line 1 "ds/node_pool.hpp"
// マルチテストケースでも確保済み chunk を再利用する
template <class Node>
struct Node_Pool {
  union Slot {
    Node node;
    Slot* next;

    Slot() {}
    ~Slot() {}
  };
  using np = Node*;

  static constexpr int CHUNK_SIZE = 1 << 12;

  vc<unique_ptr<Slot[]>> chunks;
  int chunk_id = 0;
  int pos = 0;
  Slot* free_head = nullptr;

  ~Node_Pool() {
    auto& cache = chunk_cache();
    for (auto& p : chunks) cache.eb(std::move(p));
  }

  template <class... Args>
  np create(Args&&... args) {
    Slot* s = new_slot();
    return ::new (&s->node) Node(forward<Args>(args)...);
  }

  np clone(const np x) {
    assert(x);
    Slot* s = new_slot();
    return ::new (&s->node) Node(*x);
  }

  void destroy(np x) {
    if (!x) return;
    x->~Node();
    Slot* s = reinterpret_cast<Slot*>(x);
    s->next = free_head;
    free_head = s;
  }

  // 全 node を無効化する。
  // 確保済み chunk は解放せず、次回以降に再利用する。
  void reset() {
    free_head = nullptr;
    chunk_id = 0;
    pos = 0;
  }

 private:
  static vc<unique_ptr<Slot[]>>& chunk_cache() {
    // static Node_Pool の destructor より先に破棄されないようにする。
    static auto* cache = new vc<unique_ptr<Slot[]>>();
    return *cache;
  }

  void alloc_chunk() {
    auto& cache = chunk_cache();
    if (cache.empty()) {
      chunks.eb(make_unique<Slot[]>(CHUNK_SIZE));
    } else {
      chunks.eb(std::move(cache.back()));
      cache.pop_back();
    }
  }

  Slot* new_slot() {
    if (free_head) {
      Slot* s = free_head;
      free_head = free_head->next;
      return s;
    }

    if (chunk_id == len(chunks)) alloc_chunk();

    Slot* s = &chunks[chunk_id][pos++];
    if (pos == CHUNK_SIZE) {
      ++chunk_id;
      pos = 0;
    }
    return s;
  }
};
#line 4 "ds/segtree/sortable_segtree.hpp"

template <typename Monoid>
struct Sortable_SegTree {
  using MX = Monoid;
  using X = typename MX::value_type;
  const int N, KEY_MAX;

  struct Node {
    X x, rev_x;
    int size;
    Node *l, *r;
  };
  Node_Pool<Node> pool;
  using np = Node*;

  FastSet ss;       // 区間の左端全体を表す fastset
  SegTree<MX> seg;  // 区間を集約した値を区間の左端にのせた segtree
  vector<np> root;  // 区間の左端に、dynamic segtree の node を乗せる
  vector<bool> rev;

  Sortable_SegTree(int KEY_MAX, vector<int> key, vector<X> dat)
      : N(key.size()), KEY_MAX(KEY_MAX), ss(key.size()), seg(dat) {
    init(key, dat);
  }
  void set(int i, int key, const X& x) {
    assert(key < KEY_MAX);
    split_at(i), split_at(i + 1);
    rev[i] = 0, root[i] = new_node();
    set_rec(root[i], 0, KEY_MAX, key, x);
    seg.set(i, x);
  }

  X prod_all() { return seg.prod_all(); }

  X prod(int l, int r) {
    split_at(l), split_at(r);
    return seg.prod(l, r);
  }

  void sort_inc(int l, int r) {
    split_at(l), split_at(r);
    while (1) {
      np c = root[l];
      int i = ss.next(l + 1);
      if (i == r) break;
      root[l] = merge(c, root[i]);
      ss.erase(i), seg.set(i, MX::id());
    }
    rev[l] = 0, seg.set(l, root[l]->x);
  };

  void sort_dec(int l, int r) {
    sort_inc(l, r), rev[l] = 1;
    seg.set(l, root[l]->rev_x);
  };

  pair<vc<int>, vc<X>> get_all() {
    vector<int> key;
    vector<X> dat;
    key.reserve(N);
    dat.reserve(N);
    auto dfs = [&](auto& dfs, np n, int l, int r, bool rev) -> void {
      if (!n) return;
      if (r == l + 1) {
        key.eb(l), dat.eb(n->x);
        return;
      }
      int m = (l + r) / 2;
      if (!rev) {
        dfs(dfs, n->l, l, m, rev), dfs(dfs, n->r, m, r, rev);
      }
      if (rev) {
        dfs(dfs, n->r, m, r, rev), dfs(dfs, n->l, l, m, rev);
      }
    };
    for (int i = 0; i < N; ++i) {
      if (ss[i]) dfs(dfs, root[i], 0, KEY_MAX, rev[i]);
    }
    return {key, dat};
  }

 private:
  void init(vector<int>& key, vector<X>& dat) {
    rev.assign(N, 0), root.clear(), root.reserve(N);
    seg.build(N, [&](int i) -> X { return dat[i]; });
    for (int i = 0; i < N; ++i) {
      ss.insert(i);
      root.eb(new_node(MX::id()));
      assert(key[i] < KEY_MAX);
      set_rec(root[i], 0, KEY_MAX, key[i], dat[i]);
    }
  }

  // x が左端になるようにする
  void split_at(int x) {
    if (x == N || ss[x]) return;
    int a = ss.prev(x), b = ss.next(a + 1);
    ss.insert(x);
    if (!rev[a]) {
      auto [nl, nr] = split(root[a], x - a);
      root[a] = nl, root[x] = nr;
      rev[a] = rev[x] = 0;
      seg.set(a, root[a]->x), seg.set(x, root[x]->x);
    } else {
      auto [nl, nr] = split(root[a], b - x);
      root[a] = nr, root[x] = nl;
      rev[a] = rev[x] = 1;
      seg.set(a, root[a]->rev_x), seg.set(x, root[x]->rev_x);
    }
  }

  void rebuild() {
    auto [key, dat] = get_all();
    pool.reset();
    init(key, dat);
  }

  np new_node(X x = MX::id()) {
    np c = pool.create();
    c->x = c->rev_x = x;
    c->l = c->r = nullptr;
    c->size = 1;
    return c;
  }

  pair<np, np> split(np n, int k) {
    if (k == 0) {
      return {nullptr, n};
    }
    if (k == n->size) {
      return {n, nullptr};
    }
    int s = (n->l ? n->l->size : 0);
    Node* b = new_node();
    if (k <= s) {
      auto [nl, nr] = split(n->l, k);
      b->l = nr, b->r = n->r, n->l = nl, n->r = nullptr;
    }
    if (k > s) {
      auto [nl, nr] = split(n->r, k - s);
      n->l = n->l, n->r = nl, b->l = nullptr, b->r = nr;
    }
    update(n), update(b);
    return {n, b};
  }

  np merge(np a, np b) {
    if (!a) return b;
    if (!b) return a;
    a->l = merge(a->l, b->l), a->r = merge(a->r, b->r);
    update(a);
    return a;
  }

  void update(np n) {
    if (!(n->l) && !(n->r)) {
      return;
    }
    if (!(n->l)) {
      n->x = n->r->x, n->rev_x = n->r->rev_x, n->size = n->r->size;
      return;
    }
    if (!(n->r)) {
      n->x = n->l->x, n->rev_x = n->l->rev_x, n->size = n->l->size;
      return;
    }
    n->x = MX::op(n->l->x, n->r->x);
    n->rev_x = MX::op(n->r->rev_x, n->l->rev_x);
    n->size = n->l->size + n->r->size;
  }

  void set_rec(np n, int l, int r, int k, const X& x) {
    if (r == l + 1) {
      n->x = n->rev_x = x;
      return;
    }
    int m = (l + r) / 2;
    if (k < m) {
      if (!(n->l)) n->l = new_node();
      set_rec(n->l, l, m, k, x);
    }
    if (m <= k) {
      if (!(n->r)) n->r = new_node();
      set_rec(n->r, m, r, k, x);
    }
    update(n);
  }
};
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