blob: d6832b3e92d2569917f09f6d450715d83d31578b (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
|
#include <cstring>
#include <iostream>
const int MAX = 1000010; // Why 1000001 is not ok!?
int n;
int H[100001];
int bit[MAX];
int reverse_pairs[100001];
int lowbit(int x) { return x & -x; }
void add(int x, int y) {
for (int i = x; i < MAX; i += lowbit(i)) {
bit[i] += y;
}
}
int query(int x) {
int result = 0;
for (int i = x; i != 0; i -= lowbit(i)) {
result += bit[i];
}
return result;
}
int main() {
std::ios_base::sync_with_stdio(false);
std::cin.tie(nullptr);
std::cin >> n;
for (int i = 1; i <= n; i++) {
std::cin >> H[i];
H[i]++;
}
for (int i = 1; i <= n; i++) {
add(H[i], 1);
reverse_pairs[i] = i - query(H[i]);
}
std::memset(bit, 0, sizeof bit);
for (int i = n; i >= 1; i--) {
add(H[i], 1);
reverse_pairs[i] += query(H[i] - 1);
}
long long result = 0;
for (int i = 1; i <= n; i++) {
result += (1LL + reverse_pairs[i]) * reverse_pairs[i] / 2;
}
std::cout << result;
return 0;
}
|
