Submission #526195

# Submission time Handle Problem Language Result Execution time Memory
526195 2022-02-13T22:40:18 Z Plurm Diversity (CEOI21_diversity) C++11
64 / 100
7000 ms 9924 KB
#include <bits/stdc++.h>
using namespace std;

template <typename T>
class FenwickTree{
public:
  T* FT;
  int n;
  bool negmode;
  FenwickTree(int sz = 1 << 19, bool negindex = true){
    n = sz+505;
    FT = new T[n];
    fill(FT, FT+n, (T)0);
    negmode = negindex;
  }
  void add(int idx, T amt){
    if(negmode) idx += n/2;
    while(idx < n){
      FT[idx] += amt;
      idx += idx & -idx;
    }
  }
  T sum(int idx){
    if(negmode) idx += n/2;
    T ret = (T)0;
    while(idx > 0){
      ret += FT[idx];
      idx -= idx & -idx;
    }
    return ret;
  }
  int lower_bound(const int v){
    if(v > FT[1]) return 0;
    int cur = 1 << 18;
    int part = FT[cur];
    for(int i = 17; i >= 0; i--){
      if(part >= v){
        cur += 1 << i;
        part += FT[cur];
      }else{
        part -= FT[cur];
        cur -= 1 << i;
        part += FT[cur];
      }
    }
    if(part < v) return cur-1;
    return cur;
  }
  int upper_bound(const int v){
    return lower_bound(v+1);
  }
};

FenwickTree<int> FT1; // Ri
FenwickTree<long long> FT2; // Ri * i
int cnt[300005];
int a[300005];
// abstract deque
// fenwick indexing:
// [...] [-3] [-2] [-1] [0] [1] [2] [...]
// deque indexing:
// [...] [6] [4] [2] [1] [3] [5] [...]
// invariant:
// dq[-i] <= dq[i] for all positive i
// dq[-i] >= dq[i+1] for all positive i

int dq2fw(int idx){
  return idx/2 * (idx % 2 ? 1 : -1);
}

FenwickTree<int> dq(300000, false); // using deque indexing
long long deque_add(const int x){
  int idx = dq.upper_bound(x)+1;
  dq.add(idx, 1);
  dq.add(idx+1, -1);
  int b = dq2fw(idx);
  FT1.add(b, 1);
  FT2.add(b, b);
  return FT2.FT[1 << 19] - FT2.sum(b) - 1ll * (b-1) * (FT1.FT[1 << 19] - FT1.sum(b))
  + 1ll * (b+1) * FT1.sum(b-1) - FT2.sum(b-1) + x+1;
}
long long deque_remove(const int x){
  int idx = dq.lower_bound(x);
  dq.add(idx, -1);
  dq.add(idx+1, 1);
  int b = dq2fw(idx);
  FT1.add(b, -1);
  FT2.add(b, -b);
  return FT2.FT[1 << 19] - FT2.sum(b) - 1ll * (b-1) * (FT1.FT[1 << 19] - FT1.sum(b))
  + 1ll * (b+1) * FT1.sum(b-1) - FT2.sum(b-1) + x;
}

vector<tuple<int,int,int>> qbckt[2048]; // (L, R, Q)
long long answer[50005];
int qcnt[2048];

int main(){
	int n,q;
	scanf("%d%d",&n,&q);
	for(int i = 1; i <= n; i++){
		scanf("%d",a+i);
	}
  int SQRT = 1333;
  vector<pair<int,int>> rawq;
  for(int i = 0; i < q; i++){
    int l, r;
    scanf("%d%d",&l,&r);
    rawq.emplace_back(l,r);
    qcnt[l/SQRT]++;
  }
  for(int i = 0; i <= n/SQRT+2; i++){
    qbckt[i].reserve(qcnt[i]);
  }
  for(int i = 0; i < q; i++){
    int l, r;
    tie(l, r) = rawq[i];
    qbckt[l / SQRT].emplace_back(l, r, i);
  }
  int lptr = 1;
  int rptr = 0;
  long long ans = 0ll;
  for(int i = 0; i <= n/SQRT+2; i++){
    sort(qbckt[i].begin(), qbckt[i].end(), [](tuple<int,int,int> x, tuple<int,int,int> y){
      return get<1>(x) < get<1>(y);
    });
    // Below goes declaratively.
    for(auto qr : qbckt[i]){
      int l, r, qnum;
      tie(l, r, qnum) = qr;
      while(rptr < r){
        rptr++;
        ans += deque_add(cnt[a[rptr]]);
        cnt[a[rptr]]++;
      }
      while(lptr > l){
        lptr--;
        ans += deque_add(cnt[a[lptr]]);
        cnt[a[lptr]]++;
      }
      while(lptr < l){
        ans -= deque_remove(cnt[a[lptr]]);
        cnt[a[lptr]]--;
        lptr++;
      }
      while(rptr > r){
        ans -= deque_remove(cnt[a[rptr]]);
        cnt[a[rptr]]--;
        rptr--;
      }
      answer[qnum] = ans;
    }
  }
  for(int i = 0; i < q; i++){
    printf("%lld\n", answer[i]);
  }
	return 0;
}

Compilation message

diversity.cpp: In function 'int main()':
diversity.cpp:99:7: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   99 |  scanf("%d%d",&n,&q);
      |  ~~~~~^~~~~~~~~~~~~~
diversity.cpp:101:8: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
  101 |   scanf("%d",a+i);
      |   ~~~~~^~~~~~~~~~
diversity.cpp:107:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
  107 |     scanf("%d%d",&l,&r);
      |     ~~~~~^~~~~~~~~~~~~~
# Verdict Execution time Memory Grader output
1 Correct 3 ms 7628 KB Output is correct
2 Correct 4 ms 7628 KB Output is correct
3 Correct 5 ms 7628 KB Output is correct
4 Correct 3 ms 7628 KB Output is correct
5 Correct 4 ms 7628 KB Output is correct
6 Correct 3 ms 7628 KB Output is correct
7 Correct 4 ms 7628 KB Output is correct
8 Correct 3 ms 7628 KB Output is correct
9 Correct 3 ms 7628 KB Output is correct
10 Correct 3 ms 7628 KB Output is correct
# Verdict Execution time Memory Grader output
1 Correct 3 ms 7628 KB Output is correct
2 Correct 3 ms 7628 KB Output is correct
3 Correct 6 ms 7756 KB Output is correct
4 Correct 31 ms 8084 KB Output is correct
5 Correct 61 ms 8380 KB Output is correct
6 Correct 83 ms 8844 KB Output is correct
7 Correct 100 ms 8856 KB Output is correct
8 Correct 106 ms 8864 KB Output is correct
9 Correct 87 ms 8864 KB Output is correct
10 Correct 87 ms 8856 KB Output is correct
11 Correct 84 ms 8868 KB Output is correct
12 Correct 95 ms 8864 KB Output is correct
13 Correct 87 ms 8864 KB Output is correct
14 Correct 84 ms 8856 KB Output is correct
15 Correct 92 ms 8776 KB Output is correct
# Verdict Execution time Memory Grader output
1 Correct 3 ms 7628 KB Output is correct
2 Correct 3 ms 7628 KB Output is correct
3 Correct 6 ms 7756 KB Output is correct
4 Correct 31 ms 8084 KB Output is correct
5 Correct 61 ms 8380 KB Output is correct
6 Correct 83 ms 8844 KB Output is correct
7 Correct 100 ms 8856 KB Output is correct
8 Correct 106 ms 8864 KB Output is correct
9 Correct 87 ms 8864 KB Output is correct
10 Correct 87 ms 8856 KB Output is correct
11 Correct 84 ms 8868 KB Output is correct
12 Correct 95 ms 8864 KB Output is correct
13 Correct 87 ms 8864 KB Output is correct
14 Correct 84 ms 8856 KB Output is correct
15 Correct 92 ms 8776 KB Output is correct
16 Correct 3 ms 7628 KB Output is correct
17 Correct 4 ms 7628 KB Output is correct
18 Correct 6 ms 7752 KB Output is correct
19 Correct 37 ms 8100 KB Output is correct
20 Correct 60 ms 8492 KB Output is correct
21 Correct 85 ms 8780 KB Output is correct
22 Correct 94 ms 8780 KB Output is correct
23 Correct 88 ms 8860 KB Output is correct
24 Correct 98 ms 8860 KB Output is correct
25 Correct 102 ms 8916 KB Output is correct
26 Correct 86 ms 8856 KB Output is correct
27 Correct 89 ms 8856 KB Output is correct
28 Correct 91 ms 8772 KB Output is correct
29 Correct 101 ms 8860 KB Output is correct
30 Correct 89 ms 8860 KB Output is correct
# Verdict Execution time Memory Grader output
1 Correct 3 ms 7628 KB Output is correct
2 Correct 3 ms 7628 KB Output is correct
3 Correct 6 ms 7756 KB Output is correct
4 Correct 31 ms 8084 KB Output is correct
5 Correct 61 ms 8380 KB Output is correct
6 Correct 83 ms 8844 KB Output is correct
7 Correct 100 ms 8856 KB Output is correct
8 Correct 106 ms 8864 KB Output is correct
9 Correct 87 ms 8864 KB Output is correct
10 Correct 87 ms 8856 KB Output is correct
11 Correct 84 ms 8868 KB Output is correct
12 Correct 95 ms 8864 KB Output is correct
13 Correct 87 ms 8864 KB Output is correct
14 Correct 84 ms 8856 KB Output is correct
15 Correct 92 ms 8776 KB Output is correct
16 Correct 3 ms 7628 KB Output is correct
17 Correct 4 ms 7628 KB Output is correct
18 Correct 6 ms 7752 KB Output is correct
19 Correct 37 ms 8100 KB Output is correct
20 Correct 60 ms 8492 KB Output is correct
21 Correct 85 ms 8780 KB Output is correct
22 Correct 94 ms 8780 KB Output is correct
23 Correct 88 ms 8860 KB Output is correct
24 Correct 98 ms 8860 KB Output is correct
25 Correct 102 ms 8916 KB Output is correct
26 Correct 86 ms 8856 KB Output is correct
27 Correct 89 ms 8856 KB Output is correct
28 Correct 91 ms 8772 KB Output is correct
29 Correct 101 ms 8860 KB Output is correct
30 Correct 89 ms 8860 KB Output is correct
31 Correct 4 ms 7628 KB Output is correct
32 Correct 4 ms 7628 KB Output is correct
33 Correct 3 ms 7628 KB Output is correct
34 Correct 6 ms 7756 KB Output is correct
35 Correct 8 ms 7756 KB Output is correct
36 Correct 6 ms 7756 KB Output is correct
37 Correct 21 ms 7884 KB Output is correct
38 Correct 18 ms 7904 KB Output is correct
39 Correct 34 ms 8072 KB Output is correct
40 Correct 61 ms 8492 KB Output is correct
41 Correct 87 ms 8860 KB Output is correct
42 Correct 96 ms 8856 KB Output is correct
43 Correct 92 ms 8860 KB Output is correct
44 Correct 96 ms 8860 KB Output is correct
45 Correct 88 ms 8856 KB Output is correct
46 Correct 90 ms 8784 KB Output is correct
47 Correct 101 ms 8856 KB Output is correct
48 Correct 92 ms 8864 KB Output is correct
49 Correct 92 ms 8856 KB Output is correct
50 Correct 93 ms 8852 KB Output is correct
51 Correct 119 ms 8772 KB Output is correct
52 Correct 95 ms 8824 KB Output is correct
53 Correct 90 ms 8836 KB Output is correct
54 Correct 101 ms 8820 KB Output is correct
55 Correct 96 ms 8780 KB Output is correct
56 Correct 85 ms 8868 KB Output is correct
57 Correct 92 ms 8860 KB Output is correct
58 Correct 91 ms 8856 KB Output is correct
59 Correct 89 ms 8872 KB Output is correct
60 Correct 90 ms 8812 KB Output is correct
# Verdict Execution time Memory Grader output
1 Correct 3 ms 7628 KB Output is correct
2 Correct 4 ms 7628 KB Output is correct
3 Correct 5 ms 7628 KB Output is correct
4 Correct 3 ms 7628 KB Output is correct
5 Correct 4 ms 7628 KB Output is correct
6 Correct 3 ms 7628 KB Output is correct
7 Correct 4 ms 7628 KB Output is correct
8 Correct 3 ms 7628 KB Output is correct
9 Correct 3 ms 7628 KB Output is correct
10 Correct 3 ms 7628 KB Output is correct
11 Correct 3 ms 7628 KB Output is correct
12 Correct 3 ms 7628 KB Output is correct
13 Correct 6 ms 7756 KB Output is correct
14 Correct 31 ms 8084 KB Output is correct
15 Correct 61 ms 8380 KB Output is correct
16 Correct 83 ms 8844 KB Output is correct
17 Correct 100 ms 8856 KB Output is correct
18 Correct 106 ms 8864 KB Output is correct
19 Correct 87 ms 8864 KB Output is correct
20 Correct 87 ms 8856 KB Output is correct
21 Correct 84 ms 8868 KB Output is correct
22 Correct 95 ms 8864 KB Output is correct
23 Correct 87 ms 8864 KB Output is correct
24 Correct 84 ms 8856 KB Output is correct
25 Correct 92 ms 8776 KB Output is correct
26 Correct 3 ms 7628 KB Output is correct
27 Correct 4 ms 7628 KB Output is correct
28 Correct 6 ms 7752 KB Output is correct
29 Correct 37 ms 8100 KB Output is correct
30 Correct 60 ms 8492 KB Output is correct
31 Correct 85 ms 8780 KB Output is correct
32 Correct 94 ms 8780 KB Output is correct
33 Correct 88 ms 8860 KB Output is correct
34 Correct 98 ms 8860 KB Output is correct
35 Correct 102 ms 8916 KB Output is correct
36 Correct 86 ms 8856 KB Output is correct
37 Correct 89 ms 8856 KB Output is correct
38 Correct 91 ms 8772 KB Output is correct
39 Correct 101 ms 8860 KB Output is correct
40 Correct 89 ms 8860 KB Output is correct
41 Correct 4 ms 7628 KB Output is correct
42 Correct 4 ms 7628 KB Output is correct
43 Correct 3 ms 7628 KB Output is correct
44 Correct 6 ms 7756 KB Output is correct
45 Correct 8 ms 7756 KB Output is correct
46 Correct 6 ms 7756 KB Output is correct
47 Correct 21 ms 7884 KB Output is correct
48 Correct 18 ms 7904 KB Output is correct
49 Correct 34 ms 8072 KB Output is correct
50 Correct 61 ms 8492 KB Output is correct
51 Correct 87 ms 8860 KB Output is correct
52 Correct 96 ms 8856 KB Output is correct
53 Correct 92 ms 8860 KB Output is correct
54 Correct 96 ms 8860 KB Output is correct
55 Correct 88 ms 8856 KB Output is correct
56 Correct 90 ms 8784 KB Output is correct
57 Correct 101 ms 8856 KB Output is correct
58 Correct 92 ms 8864 KB Output is correct
59 Correct 92 ms 8856 KB Output is correct
60 Correct 93 ms 8852 KB Output is correct
61 Correct 119 ms 8772 KB Output is correct
62 Correct 95 ms 8824 KB Output is correct
63 Correct 90 ms 8836 KB Output is correct
64 Correct 101 ms 8820 KB Output is correct
65 Correct 96 ms 8780 KB Output is correct
66 Correct 85 ms 8868 KB Output is correct
67 Correct 92 ms 8860 KB Output is correct
68 Correct 91 ms 8856 KB Output is correct
69 Correct 89 ms 8872 KB Output is correct
70 Correct 90 ms 8812 KB Output is correct
71 Correct 19 ms 7884 KB Output is correct
72 Correct 20 ms 7916 KB Output is correct
73 Correct 25 ms 7884 KB Output is correct
74 Correct 18 ms 7868 KB Output is correct
75 Correct 22 ms 7900 KB Output is correct
76 Correct 33 ms 8092 KB Output is correct
77 Correct 35 ms 8012 KB Output is correct
78 Correct 34 ms 8036 KB Output is correct
79 Correct 34 ms 8012 KB Output is correct
80 Correct 33 ms 8012 KB Output is correct
81 Correct 65 ms 8480 KB Output is correct
82 Correct 64 ms 8408 KB Output is correct
83 Correct 67 ms 8576 KB Output is correct
84 Correct 66 ms 8508 KB Output is correct
85 Correct 63 ms 8524 KB Output is correct
86 Correct 69 ms 8536 KB Output is correct
87 Correct 65 ms 8552 KB Output is correct
88 Correct 66 ms 8548 KB Output is correct
89 Correct 72 ms 8504 KB Output is correct
90 Correct 69 ms 8648 KB Output is correct
91 Correct 98 ms 9256 KB Output is correct
92 Correct 96 ms 9248 KB Output is correct
93 Correct 94 ms 9228 KB Output is correct
94 Correct 99 ms 9156 KB Output is correct
95 Correct 106 ms 9248 KB Output is correct
96 Correct 94 ms 9540 KB Output is correct
97 Correct 93 ms 9540 KB Output is correct
98 Correct 96 ms 9588 KB Output is correct
99 Correct 94 ms 9548 KB Output is correct
100 Correct 101 ms 9640 KB Output is correct
101 Correct 102 ms 9744 KB Output is correct
102 Correct 92 ms 9656 KB Output is correct
103 Correct 93 ms 9548 KB Output is correct
104 Correct 113 ms 9592 KB Output is correct
105 Correct 111 ms 9568 KB Output is correct
106 Correct 96 ms 9840 KB Output is correct
107 Correct 90 ms 9840 KB Output is correct
108 Correct 89 ms 9808 KB Output is correct
109 Correct 90 ms 9752 KB Output is correct
110 Correct 90 ms 9836 KB Output is correct
111 Correct 89 ms 9836 KB Output is correct
112 Correct 94 ms 9924 KB Output is correct
113 Correct 89 ms 9804 KB Output is correct
114 Correct 90 ms 9836 KB Output is correct
115 Correct 91 ms 9840 KB Output is correct
# Verdict Execution time Memory Grader output
1 Correct 3 ms 7628 KB Output is correct
2 Correct 4 ms 7628 KB Output is correct
3 Correct 5 ms 7628 KB Output is correct
4 Correct 3 ms 7628 KB Output is correct
5 Correct 4 ms 7628 KB Output is correct
6 Correct 3 ms 7628 KB Output is correct
7 Correct 4 ms 7628 KB Output is correct
8 Correct 3 ms 7628 KB Output is correct
9 Correct 3 ms 7628 KB Output is correct
10 Correct 3 ms 7628 KB Output is correct
11 Correct 3 ms 7628 KB Output is correct
12 Correct 3 ms 7628 KB Output is correct
13 Correct 6 ms 7756 KB Output is correct
14 Correct 31 ms 8084 KB Output is correct
15 Correct 61 ms 8380 KB Output is correct
16 Correct 83 ms 8844 KB Output is correct
17 Correct 100 ms 8856 KB Output is correct
18 Correct 106 ms 8864 KB Output is correct
19 Correct 87 ms 8864 KB Output is correct
20 Correct 87 ms 8856 KB Output is correct
21 Correct 84 ms 8868 KB Output is correct
22 Correct 95 ms 8864 KB Output is correct
23 Correct 87 ms 8864 KB Output is correct
24 Correct 84 ms 8856 KB Output is correct
25 Correct 92 ms 8776 KB Output is correct
26 Correct 3 ms 7628 KB Output is correct
27 Correct 4 ms 7628 KB Output is correct
28 Correct 6 ms 7752 KB Output is correct
29 Correct 37 ms 8100 KB Output is correct
30 Correct 60 ms 8492 KB Output is correct
31 Correct 85 ms 8780 KB Output is correct
32 Correct 94 ms 8780 KB Output is correct
33 Correct 88 ms 8860 KB Output is correct
34 Correct 98 ms 8860 KB Output is correct
35 Correct 102 ms 8916 KB Output is correct
36 Correct 86 ms 8856 KB Output is correct
37 Correct 89 ms 8856 KB Output is correct
38 Correct 91 ms 8772 KB Output is correct
39 Correct 101 ms 8860 KB Output is correct
40 Correct 89 ms 8860 KB Output is correct
41 Correct 4 ms 7628 KB Output is correct
42 Correct 4 ms 7628 KB Output is correct
43 Correct 3 ms 7628 KB Output is correct
44 Correct 6 ms 7756 KB Output is correct
45 Correct 8 ms 7756 KB Output is correct
46 Correct 6 ms 7756 KB Output is correct
47 Correct 21 ms 7884 KB Output is correct
48 Correct 18 ms 7904 KB Output is correct
49 Correct 34 ms 8072 KB Output is correct
50 Correct 61 ms 8492 KB Output is correct
51 Correct 87 ms 8860 KB Output is correct
52 Correct 96 ms 8856 KB Output is correct
53 Correct 92 ms 8860 KB Output is correct
54 Correct 96 ms 8860 KB Output is correct
55 Correct 88 ms 8856 KB Output is correct
56 Correct 90 ms 8784 KB Output is correct
57 Correct 101 ms 8856 KB Output is correct
58 Correct 92 ms 8864 KB Output is correct
59 Correct 92 ms 8856 KB Output is correct
60 Correct 93 ms 8852 KB Output is correct
61 Correct 119 ms 8772 KB Output is correct
62 Correct 95 ms 8824 KB Output is correct
63 Correct 90 ms 8836 KB Output is correct
64 Correct 101 ms 8820 KB Output is correct
65 Correct 96 ms 8780 KB Output is correct
66 Correct 85 ms 8868 KB Output is correct
67 Correct 92 ms 8860 KB Output is correct
68 Correct 91 ms 8856 KB Output is correct
69 Correct 89 ms 8872 KB Output is correct
70 Correct 90 ms 8812 KB Output is correct
71 Correct 19 ms 7884 KB Output is correct
72 Correct 20 ms 7916 KB Output is correct
73 Correct 25 ms 7884 KB Output is correct
74 Correct 18 ms 7868 KB Output is correct
75 Correct 22 ms 7900 KB Output is correct
76 Correct 33 ms 8092 KB Output is correct
77 Correct 35 ms 8012 KB Output is correct
78 Correct 34 ms 8036 KB Output is correct
79 Correct 34 ms 8012 KB Output is correct
80 Correct 33 ms 8012 KB Output is correct
81 Correct 65 ms 8480 KB Output is correct
82 Correct 64 ms 8408 KB Output is correct
83 Correct 67 ms 8576 KB Output is correct
84 Correct 66 ms 8508 KB Output is correct
85 Correct 63 ms 8524 KB Output is correct
86 Correct 69 ms 8536 KB Output is correct
87 Correct 65 ms 8552 KB Output is correct
88 Correct 66 ms 8548 KB Output is correct
89 Correct 72 ms 8504 KB Output is correct
90 Correct 69 ms 8648 KB Output is correct
91 Correct 98 ms 9256 KB Output is correct
92 Correct 96 ms 9248 KB Output is correct
93 Correct 94 ms 9228 KB Output is correct
94 Correct 99 ms 9156 KB Output is correct
95 Correct 106 ms 9248 KB Output is correct
96 Correct 94 ms 9540 KB Output is correct
97 Correct 93 ms 9540 KB Output is correct
98 Correct 96 ms 9588 KB Output is correct
99 Correct 94 ms 9548 KB Output is correct
100 Correct 101 ms 9640 KB Output is correct
101 Correct 102 ms 9744 KB Output is correct
102 Correct 92 ms 9656 KB Output is correct
103 Correct 93 ms 9548 KB Output is correct
104 Correct 113 ms 9592 KB Output is correct
105 Correct 111 ms 9568 KB Output is correct
106 Correct 96 ms 9840 KB Output is correct
107 Correct 90 ms 9840 KB Output is correct
108 Correct 89 ms 9808 KB Output is correct
109 Correct 90 ms 9752 KB Output is correct
110 Correct 90 ms 9836 KB Output is correct
111 Correct 89 ms 9836 KB Output is correct
112 Correct 94 ms 9924 KB Output is correct
113 Correct 89 ms 9804 KB Output is correct
114 Correct 90 ms 9836 KB Output is correct
115 Correct 91 ms 9840 KB Output is correct
116 Correct 4986 ms 9492 KB Output is correct
117 Correct 4639 ms 9488 KB Output is correct
118 Correct 4894 ms 9772 KB Output is correct
119 Correct 5364 ms 9776 KB Output is correct
120 Correct 5197 ms 9772 KB Output is correct
121 Execution timed out 7059 ms 9360 KB Time limit exceeded
122 Halted 0 ms 0 KB -