蓝桥杯 小朋友排队

1 #include <iostream>
2 #include <cstdio>
3 #include <cstring>
4 using namespace std;
5 typedef long long ll;
6
7 const int N = 100000;
8 const int H = 1000000;
9 int bit[H + 5], a[N + 5], cnt[N + 5];
10 ll u[N + 5];
11
12 void add(int i, int x)
13 {
14     while (i <= H)
15     {
16         bit[i] += x;
17         i += i & -i;
18     }
19 }
20
21 int sum(int i)
22 {
23     int s = 0;
24     while (i)
25     {
26         s += bit[i];
27         i -= i & -i;
28     }
29     return s;
30 }
31
32 void init()
33 {
34     for (int i = 1; i <= N; i++)
35     {
36         u[i] = u[i - 1] + (ll)i;
37     }
38 }
39
40 int main()
41 {
42     int n, tmp;
43     init();
44     cin >> n;
45     for (int i = 0; i < n; i++)
46     {
47         scanf("%d", &a[i]);
48         a[i]++;
49         add(a[i], 1);
50         cnt[i] = i + 1 - sum(a[i]);
51     }
52     memset(bit, 0, sizeof(bit));
53     for (int i = n - 1; i >= 0; i--)
54     {
55         add(a[i], 1);
56         cnt[i] += sum(a[i] - 1);
57     }
58     ll ans = 0;
59     for (int i = 0; i < n; i++)
60     {
61         ans += u[cnt[i]];
62     }
63     cout << ans << endl;
64     return 0;
65 }