oj.uz

Submission #252952

# Submission time Handle Problem Language Result Execution time Memory
252952 2020-07-26T14:16:03 Z EntityIT New Home (APIO18_new_home) C++14
80 / 100
 5000 ms 551168 KB 
#include <bits/stdc++.h>
using namespace std;

#define ALL(x) (x).begin(), (x).end()
#define SZ(x) static_cast<int>((x).size())

template<class T, size_t D>
struct vec : vector<vec<T, D - 1>> {
  template<class... Args>
  vec(size_t n = 0, Args... args)
      : vector<vec<T, D - 1>>(n, vec<T, D - 1>(args...)) {}
};
template<class T>
struct vec<T, 1> : vector<T> {
  template<class... Args>
  vec(Args... args)
      : vector<T>(args...) {}
};

template<class T>
inline bool Minimize(T& a, const T& b) { return a > b ? a = b, true : false; }
template<class T>
inline bool Maximize(T& a, const T& b) { return a < b ? a = b, true : false; }
inline int Next(int i, int n) { return i == n - 1 ? 0 : i + 1; }
inline int Prev(int i, int n) { return !i ? n - 1 : i - 1; }

mt19937 rng(static_cast<uint32_t>(chrono::steady_clock::now().time_since_epoch().count()));

struct IT {
  int n;
  struct Node {
    array<vec<pair<int, int>, 1>, 2> segments;
    vec<pair<int, int>, 1> queries;
    Node()
        : segments({}),
          queries({}) {}
  };
  vec<Node, 1> nodes;
  IT(int t_n, const vec<pair<int, int>, 2>& queries_time_marks)
      : n(t_n),
        nodes(n << 1) {
    for (int i = 0; i < n; ++i) {
      nodes[i + n].queries = queries_time_marks[i];
    }
    for (int i = n - 1; i; --i) {
      merge(ALL(nodes[i << 1].queries), ALL(nodes[i << 1 | 1].queries), back_inserter(nodes[i].queries));
    }
  }

  void InsertSegment(int be, int en, bool slope, pair<int, int> val) {
    for (be += n, en += n; be < en; be >>= 1, en >>= 1) {
      if (be & 1) {
        nodes[be++].segments[slope].emplace_back(val);
      }
      if (en & 1) {
        nodes[--en].segments[slope].emplace_back(val);
      }
    }
  }
};

int main() {
  ios_base::sync_with_stdio(0); cin.tie(0);

  constexpr int kMaxX = 2e8;

  int n_stores, n_types, n_queries; cin >> n_stores >> n_types >> n_queries;

  vec<int, 1> time_marks; time_marks.reserve((n_stores << 1) + n_queries);

  vec<tuple<int, int, int, bool>, 1> changes; changes.reserve(n_stores << 1);
  while (n_stores--) {
    int x, type, l, r; cin >> x >> type >> l >> r; x <<= 1; --type;
    changes.emplace_back(l, x, type, true);
    changes.emplace_back(r + 1, x, type, false);
    time_marks.emplace_back(l);
    time_marks.emplace_back(r + 1);
  }
  sort(ALL(changes));

  vec<pair<int, int>, 1> queries(n_queries);
  for (auto& i : queries) {
    cin >> i.first >> i.second; i.first <<= 1;
    time_marks.emplace_back(i.second);
  }

  sort(ALL(time_marks));
  time_marks.erase(unique(ALL(time_marks)), time_marks.end());

  vec<int, 1> answers(n_queries);
  vec<int, 1> ord_queries(n_queries); iota(ALL(ord_queries), 0);
  sort(ALL(ord_queries), [&](int i, int j) { return queries[i].second < queries[j].second; });
  ord_queries.emplace_back(-1);
  array<vec<map<int, int>, 1>, 2> begin_times_types{vec<map<int, int>, 1>(n_types), vec<map<int, int>, 1>(n_types)};
  array<vec<tuple<int, int, int, int>, 1>, 2> segments;
  for (auto& i_query : ord_queries) {
    static auto it_changes = changes.begin();
    static int n_open_types = 0;
    static vec<map<int, int>, 1> n_occurrences_xs_types(n_types);

    for (; it_changes != changes.end() && (!~i_query || get<0>(*it_changes) <= queries[i_query].second); ++it_changes) {
      int cur_time, x, type; bool insertion; tie(cur_time, x, type, insertion) = *it_changes;
      n_open_types -= !!SZ(n_occurrences_xs_types[type]);
      cur_time = static_cast<int>(lower_bound(ALL(time_marks), cur_time) - time_marks.begin());

      auto Insert = [&](int a, int b) {
        if (!a) {
          begin_times_types[true][type][2] = cur_time;
        } else if (b > kMaxX) {
          begin_times_types[false][type][a] = cur_time;
        } else {
          begin_times_types[false][type][a] = begin_times_types[true][type][(a + b) >> 1] = cur_time;
        }
      };
      auto Erase = [&](int a, int b) {
        if (!a) {
          segments[true].emplace_back(2, b, begin_times_types[true][type][2], cur_time);
          if (get<2>(segments[true].back()) == get<3>(segments[true].back())) {
            segments[true].pop_back();
          }
        } else if (b > kMaxX) {
          segments[false].emplace_back(a, kMaxX, begin_times_types[false][type][a], cur_time);
          if (get<2>(segments[false].back()) == get<3>(segments[false].back())) {
            segments[false].pop_back();
          }
        } else {
          segments[false].emplace_back(a, (a + b) >> 1, begin_times_types[false][type][a], cur_time);
          if (get<2>(segments[false].back()) == get<3>(segments[false].back())) {
            segments[false].pop_back();
          }
          segments[true].emplace_back((a + b) >> 1, b, begin_times_types[true][type][(a + b) >> 1], cur_time);
          if (get<2>(segments[true].back()) == get<3>(segments[true].back())) {
            segments[true].pop_back();
          }
        }
      };

			auto it = n_occurrences_xs_types[type].find(x);
      if (insertion) {
        if (it == n_occurrences_xs_types[type].end()) {
					it = n_occurrences_xs_types[type].emplace(x, 1).first;
          if (it == n_occurrences_xs_types[type].begin() && next(it) == n_occurrences_xs_types[type].end()) {
            Insert(0, x); Insert(x, kMaxX + 2);
          } else if (it == n_occurrences_xs_types[type].begin()) {
            Erase(0, next(it)->first);
            Insert(0, x); Insert(x, next(it)->first);
          } else if (next(it) == n_occurrences_xs_types[type].end()) {
            Erase(prev(it)->first, kMaxX + 2);
            Insert(prev(it)->first, x); Insert(x, kMaxX + 2);
          } else {
            Erase(prev(it)->first, next(it)->first);
            Insert(prev(it)->first, x); Insert(x, next(it)->first);
          }
        } else {
					++it->second;
				}
      } else {
        if (it->second == 1) {
          if (it == n_occurrences_xs_types[type].begin() && next(it) == n_occurrences_xs_types[type].end()) {
            Erase(0, x); Erase(x, kMaxX + 2);
          } else if (it == n_occurrences_xs_types[type].begin()) {
            Erase(0, x); Erase(x, next(it)->first);
            Insert(0, next(it)->first);
          } else if (next(it) == n_occurrences_xs_types[type].end()) {
            Erase(prev(it)->first, x); Erase(x, kMaxX + 2);
            Insert(prev(it)->first, kMaxX + 2);
          } else {
            Erase(prev(it)->first, x); Erase(x, next(it)->first);
            Insert(prev(it)->first, next(it)->first);
          }
          n_occurrences_xs_types[type].erase(it);
        } else {
					--it->second;
				}
      }
      n_open_types += !!SZ(n_occurrences_xs_types[type]);
    }

    if (n_open_types != n_types && ~i_query) {
      answers[i_query] = -1;
    }
  }

  vec<pair<int, int>, 2> queries_time_marks(SZ(time_marks));
  for (int i = 0; i < n_queries; ++i) {
    if (answers[i]) {
      continue;
    }
    queries_time_marks[static_cast<int>(lower_bound(ALL(time_marks), queries[i].second) - time_marks.begin())].emplace_back(queries[i].first, i);
  }
  for (auto& queries_time_mark : queries_time_marks) {
    sort(ALL(queries_time_mark));
  }

  IT it(SZ(time_marks), queries_time_marks);

  sort(ALL(segments[true]));
  for (auto& segment : segments[true]) {
    int l_x, r_x, be_time, en_time; tie(l_x, r_x, be_time, en_time) = segment;
    it.InsertSegment(be_time, en_time, true, make_pair(l_x, r_x));
  }

  sort(ALL(segments[false]), [&](auto i, auto j) { return get<1>(i) > get<1>(j); });
  for (auto& segment : segments[false]) {
    int l_x, r_x, be_time, en_time; tie(l_x, r_x, be_time, en_time) = segment;
    it.InsertSegment(be_time, en_time, false, make_pair(l_x, r_x));
  }

  for (int i = 1; i < SZ(it.nodes); ++i) {
    int max_x = 0;
    auto it_segments = it.nodes[i].segments[true].begin();
    for (auto& query : it.nodes[i].queries) {
      for (; it_segments != it.nodes[i].segments[true].end() && it_segments->first <= query.first; ++it_segments) {
        Maximize(max_x, it_segments->second);
      }
      Maximize(answers[query.second], max_x - query.first);
    }

    int min_x = kMaxX;
    it_segments = it.nodes[i].segments[false].begin();
    reverse(ALL(it.nodes[i].queries));
    for (auto& query : it.nodes[i].queries) {
      for (; it_segments != it.nodes[i].segments[false].end() && it_segments->second >= query.first; ++it_segments) {
        Minimize(min_x, it_segments->first);
      }
      Maximize(answers[query.second], query.first - min_x);
    }
  }

  for (auto& answer : answers) {
    cout << (~answer ? answer >> 1 : -1) << '\n';
  }

  return 0;
}

Subtask #1
5.0 / 5.0

# Verdict Execution time Memory Grader output
1 Correct 0 ms 384 KB Output is correct
2 Correct 0 ms 384 KB Output is correct
3 Correct 0 ms 384 KB Output is correct
4 Correct 1 ms 384 KB Output is correct
5 Correct 1 ms 384 KB Output is correct
6 Correct 3 ms 896 KB Output is correct
7 Correct 2 ms 768 KB Output is correct
8 Correct 2 ms 896 KB Output is correct
9 Correct 2 ms 768 KB Output is correct
10 Correct 4 ms 1024 KB Output is correct
11 Correct 2 ms 768 KB Output is correct
12 Correct 3 ms 896 KB Output is correct
13 Correct 2 ms 640 KB Output is correct
14 Correct 2 ms 768 KB Output is correct
15 Correct 2 ms 896 KB Output is correct
16 Correct 2 ms 896 KB Output is correct
17 Correct 3 ms 896 KB Output is correct
18 Correct 2 ms 896 KB Output is correct
19 Correct 2 ms 896 KB Output is correct
20 Correct 2 ms 896 KB Output is correct
21 Correct 1 ms 512 KB Output is correct
22 Correct 2 ms 896 KB Output is correct
23 Correct 2 ms 896 KB Output is correct
24 Correct 3 ms 896 KB Output is correct
25 Correct 3 ms 896 KB Output is correct
26 Correct 3 ms 896 KB Output is correct
27 Correct 1 ms 512 KB Output is correct
28 Correct 2 ms 768 KB Output is correct
29 Correct 2 ms 768 KB Output is correct
30 Correct 2 ms 640 KB Output is correct

Subtask #2
7.0 / 7.0

# Verdict Execution time Memory Grader output
1 Correct 0 ms 384 KB Output is correct
2 Correct 0 ms 384 KB Output is correct
3 Correct 0 ms 384 KB Output is correct
4 Correct 1 ms 384 KB Output is correct
5 Correct 1 ms 384 KB Output is correct
6 Correct 3 ms 896 KB Output is correct
7 Correct 2 ms 768 KB Output is correct
8 Correct 2 ms 896 KB Output is correct
9 Correct 2 ms 768 KB Output is correct
10 Correct 4 ms 1024 KB Output is correct
11 Correct 2 ms 768 KB Output is correct
12 Correct 3 ms 896 KB Output is correct
13 Correct 2 ms 640 KB Output is correct
14 Correct 2 ms 768 KB Output is correct
15 Correct 2 ms 896 KB Output is correct
16 Correct 2 ms 896 KB Output is correct
17 Correct 3 ms 896 KB Output is correct
18 Correct 2 ms 896 KB Output is correct
19 Correct 2 ms 896 KB Output is correct
20 Correct 2 ms 896 KB Output is correct
21 Correct 1 ms 512 KB Output is correct
22 Correct 2 ms 896 KB Output is correct
23 Correct 2 ms 896 KB Output is correct
24 Correct 3 ms 896 KB Output is correct
25 Correct 3 ms 896 KB Output is correct
26 Correct 3 ms 896 KB Output is correct
27 Correct 1 ms 512 KB Output is correct
28 Correct 2 ms 768 KB Output is correct
29 Correct 2 ms 768 KB Output is correct
30 Correct 2 ms 640 KB Output is correct
31 Correct 978 ms 127976 KB Output is correct
32 Correct 65 ms 7560 KB Output is correct
33 Correct 984 ms 124216 KB Output is correct
34 Correct 928 ms 121432 KB Output is correct
35 Correct 949 ms 128616 KB Output is correct
36 Correct 1020 ms 128452 KB Output is correct
37 Correct 733 ms 114568 KB Output is correct
38 Correct 761 ms 115020 KB Output is correct
39 Correct 601 ms 101476 KB Output is correct
40 Correct 633 ms 104872 KB Output is correct
41 Correct 714 ms 94708 KB Output is correct
42 Correct 618 ms 86636 KB Output is correct
43 Correct 62 ms 6544 KB Output is correct
44 Correct 659 ms 92896 KB Output is correct
45 Correct 632 ms 88488 KB Output is correct
46 Correct 538 ms 79596 KB Output is correct
47 Correct 322 ms 67952 KB Output is correct
48 Correct 328 ms 70744 KB Output is correct
49 Correct 388 ms 76660 KB Output is correct
50 Correct 416 ms 81088 KB Output is correct
51 Correct 399 ms 75636 KB Output is correct

Subtask #3
10.0 / 10.0

# Verdict Execution time Memory Grader output
1 Correct 1466 ms 326344 KB Output is correct
2 Correct 1303 ms 316436 KB Output is correct
3 Correct 1275 ms 360192 KB Output is correct
4 Correct 1403 ms 332056 KB Output is correct
5 Correct 1440 ms 316136 KB Output is correct
6 Correct 1320 ms 316540 KB Output is correct
7 Correct 1291 ms 360156 KB Output is correct
8 Correct 1403 ms 331848 KB Output is correct
9 Correct 1484 ms 322228 KB Output is correct
10 Correct 1451 ms 317288 KB Output is correct
11 Correct 1190 ms 314596 KB Output is correct
12 Correct 1290 ms 316400 KB Output is correct

Subtask #4
23.0 / 23.0

# Verdict Execution time Memory Grader output
1 Correct 4126 ms 464000 KB Output is correct
2 Correct 303 ms 35044 KB Output is correct
3 Correct 3928 ms 482756 KB Output is correct
4 Correct 1608 ms 344296 KB Output is correct
5 Correct 2674 ms 373008 KB Output is correct
6 Correct 2335 ms 365672 KB Output is correct
7 Correct 4083 ms 507680 KB Output is correct
8 Correct 4030 ms 495704 KB Output is correct
9 Correct 1690 ms 380012 KB Output is correct
10 Correct 2798 ms 445464 KB Output is correct
11 Correct 3963 ms 487580 KB Output is correct
12 Correct 4006 ms 482528 KB Output is correct
13 Correct 1997 ms 393428 KB Output is correct
14 Correct 2005 ms 422668 KB Output is correct
15 Correct 2285 ms 447904 KB Output is correct
16 Correct 2640 ms 450864 KB Output is correct
17 Correct 2529 ms 426184 KB Output is correct

Subtask #5
35.0 / 35.0

# Verdict Execution time Memory Grader output
1 Correct 0 ms 384 KB Output is correct
2 Correct 0 ms 384 KB Output is correct
3 Correct 0 ms 384 KB Output is correct
4 Correct 1 ms 384 KB Output is correct
5 Correct 1 ms 384 KB Output is correct
6 Correct 3 ms 896 KB Output is correct
7 Correct 2 ms 768 KB Output is correct
8 Correct 2 ms 896 KB Output is correct
9 Correct 2 ms 768 KB Output is correct
10 Correct 4 ms 1024 KB Output is correct
11 Correct 2 ms 768 KB Output is correct
12 Correct 3 ms 896 KB Output is correct
13 Correct 2 ms 640 KB Output is correct
14 Correct 2 ms 768 KB Output is correct
15 Correct 2 ms 896 KB Output is correct
16 Correct 2 ms 896 KB Output is correct
17 Correct 3 ms 896 KB Output is correct
18 Correct 2 ms 896 KB Output is correct
19 Correct 2 ms 896 KB Output is correct
20 Correct 2 ms 896 KB Output is correct
21 Correct 1 ms 512 KB Output is correct
22 Correct 2 ms 896 KB Output is correct
23 Correct 2 ms 896 KB Output is correct
24 Correct 3 ms 896 KB Output is correct
25 Correct 3 ms 896 KB Output is correct
26 Correct 3 ms 896 KB Output is correct
27 Correct 1 ms 512 KB Output is correct
28 Correct 2 ms 768 KB Output is correct
29 Correct 2 ms 768 KB Output is correct
30 Correct 2 ms 640 KB Output is correct
31 Correct 978 ms 127976 KB Output is correct
32 Correct 65 ms 7560 KB Output is correct
33 Correct 984 ms 124216 KB Output is correct
34 Correct 928 ms 121432 KB Output is correct
35 Correct 949 ms 128616 KB Output is correct
36 Correct 1020 ms 128452 KB Output is correct
37 Correct 733 ms 114568 KB Output is correct
38 Correct 761 ms 115020 KB Output is correct
39 Correct 601 ms 101476 KB Output is correct
40 Correct 633 ms 104872 KB Output is correct
41 Correct 714 ms 94708 KB Output is correct
42 Correct 618 ms 86636 KB Output is correct
43 Correct 62 ms 6544 KB Output is correct
44 Correct 659 ms 92896 KB Output is correct
45 Correct 632 ms 88488 KB Output is correct
46 Correct 538 ms 79596 KB Output is correct
47 Correct 322 ms 67952 KB Output is correct
48 Correct 328 ms 70744 KB Output is correct
49 Correct 388 ms 76660 KB Output is correct
50 Correct 416 ms 81088 KB Output is correct
51 Correct 399 ms 75636 KB Output is correct
52 Correct 460 ms 76544 KB Output is correct
53 Correct 352 ms 75132 KB Output is correct
54 Correct 557 ms 89404 KB Output is correct
55 Correct 547 ms 93176 KB Output is correct
56 Correct 495 ms 93168 KB Output is correct
57 Correct 751 ms 94356 KB Output is correct
58 Correct 555 ms 88180 KB Output is correct
59 Correct 506 ms 86000 KB Output is correct
60 Correct 739 ms 89076 KB Output is correct
61 Correct 101 ms 28548 KB Output is correct
62 Correct 388 ms 80000 KB Output is correct
63 Correct 682 ms 88824 KB Output is correct
64 Correct 592 ms 93940 KB Output is correct
65 Correct 628 ms 99952 KB Output is correct
66 Correct 738 ms 98548 KB Output is correct
67 Correct 168 ms 23028 KB Output is correct

Subtask #6
0 / 20.0

# Verdict Execution time Memory Grader output
1 Correct 0 ms 384 KB Output is correct
2 Correct 0 ms 384 KB Output is correct
3 Correct 0 ms 384 KB Output is correct
4 Correct 1 ms 384 KB Output is correct
5 Correct 1 ms 384 KB Output is correct
6 Correct 3 ms 896 KB Output is correct
7 Correct 2 ms 768 KB Output is correct
8 Correct 2 ms 896 KB Output is correct
9 Correct 2 ms 768 KB Output is correct
10 Correct 4 ms 1024 KB Output is correct
11 Correct 2 ms 768 KB Output is correct
12 Correct 3 ms 896 KB Output is correct
13 Correct 2 ms 640 KB Output is correct
14 Correct 2 ms 768 KB Output is correct
15 Correct 2 ms 896 KB Output is correct
16 Correct 2 ms 896 KB Output is correct
17 Correct 3 ms 896 KB Output is correct
18 Correct 2 ms 896 KB Output is correct
19 Correct 2 ms 896 KB Output is correct
20 Correct 2 ms 896 KB Output is correct
21 Correct 1 ms 512 KB Output is correct
22 Correct 2 ms 896 KB Output is correct
23 Correct 2 ms 896 KB Output is correct
24 Correct 3 ms 896 KB Output is correct
25 Correct 3 ms 896 KB Output is correct
26 Correct 3 ms 896 KB Output is correct
27 Correct 1 ms 512 KB Output is correct
28 Correct 2 ms 768 KB Output is correct
29 Correct 2 ms 768 KB Output is correct
30 Correct 2 ms 640 KB Output is correct
31 Correct 978 ms 127976 KB Output is correct
32 Correct 65 ms 7560 KB Output is correct
33 Correct 984 ms 124216 KB Output is correct
34 Correct 928 ms 121432 KB Output is correct
35 Correct 949 ms 128616 KB Output is correct
36 Correct 1020 ms 128452 KB Output is correct
37 Correct 733 ms 114568 KB Output is correct
38 Correct 761 ms 115020 KB Output is correct
39 Correct 601 ms 101476 KB Output is correct
40 Correct 633 ms 104872 KB Output is correct
41 Correct 714 ms 94708 KB Output is correct
42 Correct 618 ms 86636 KB Output is correct
43 Correct 62 ms 6544 KB Output is correct
44 Correct 659 ms 92896 KB Output is correct
45 Correct 632 ms 88488 KB Output is correct
46 Correct 538 ms 79596 KB Output is correct
47 Correct 322 ms 67952 KB Output is correct
48 Correct 328 ms 70744 KB Output is correct
49 Correct 388 ms 76660 KB Output is correct
50 Correct 416 ms 81088 KB Output is correct
51 Correct 399 ms 75636 KB Output is correct
52 Correct 1466 ms 326344 KB Output is correct
53 Correct 1303 ms 316436 KB Output is correct
54 Correct 1275 ms 360192 KB Output is correct
55 Correct 1403 ms 332056 KB Output is correct
56 Correct 1440 ms 316136 KB Output is correct
57 Correct 1320 ms 316540 KB Output is correct
58 Correct 1291 ms 360156 KB Output is correct
59 Correct 1403 ms 331848 KB Output is correct
60 Correct 1484 ms 322228 KB Output is correct
61 Correct 1451 ms 317288 KB Output is correct
62 Correct 1190 ms 314596 KB Output is correct
63 Correct 1290 ms 316400 KB Output is correct
64 Correct 4126 ms 464000 KB Output is correct
65 Correct 303 ms 35044 KB Output is correct
66 Correct 3928 ms 482756 KB Output is correct
67 Correct 1608 ms 344296 KB Output is correct
68 Correct 2674 ms 373008 KB Output is correct
69 Correct 2335 ms 365672 KB Output is correct
70 Correct 4083 ms 507680 KB Output is correct
71 Correct 4030 ms 495704 KB Output is correct
72 Correct 1690 ms 380012 KB Output is correct
73 Correct 2798 ms 445464 KB Output is correct
74 Correct 3963 ms 487580 KB Output is correct
75 Correct 4006 ms 482528 KB Output is correct
76 Correct 1997 ms 393428 KB Output is correct
77 Correct 2005 ms 422668 KB Output is correct
78 Correct 2285 ms 447904 KB Output is correct
79 Correct 2640 ms 450864 KB Output is correct
80 Correct 2529 ms 426184 KB Output is correct
81 Correct 460 ms 76544 KB Output is correct
82 Correct 352 ms 75132 KB Output is correct
83 Correct 557 ms 89404 KB Output is correct
84 Correct 547 ms 93176 KB Output is correct
85 Correct 495 ms 93168 KB Output is correct
86 Correct 751 ms 94356 KB Output is correct
87 Correct 555 ms 88180 KB Output is correct
88 Correct 506 ms 86000 KB Output is correct
89 Correct 739 ms 89076 KB Output is correct
90 Correct 101 ms 28548 KB Output is correct
91 Correct 388 ms 80000 KB Output is correct
92 Correct 682 ms 88824 KB Output is correct
93 Correct 592 ms 93940 KB Output is correct
94 Correct 628 ms 99952 KB Output is correct
95 Correct 738 ms 98548 KB Output is correct
96 Correct 168 ms 23028 KB Output is correct
97 Correct 2244 ms 389880 KB Output is correct
98 Correct 348 ms 37192 KB Output is correct
99 Execution timed out 5122 ms 551168 KB Time limit exceeded
100 Halted 0 ms 0 KB -