BZOJ2348 [Baltic 2011]Plagiarism

 1 /**************************************************************
 2     Problem: 2348
 3     User: rausen
 4     Language: C++
 5     Result: Accepted
 6     Time:128 ms
 7     Memory:1196 kb
 8 ****************************************************************/
 9  
10 #include <cstdio>
11 #include <algorithm>
12  
13 using namespace std;
14 typedef long long ll;
15 typedef double lf;
16 const int N = 100005;
17 const lf eps = 1e-8;
18  
19 int n, a[N];
20 ll ans;
21  
22 inline int read() {
23     int x = 0, sgn = 1;
24     char ch = getchar();
25     while (ch < ‘0‘ || ‘9‘ < ch) {
26         if (ch == ‘-‘) sgn = -1;
27         ch = getchar();
28     }
29     while (‘0‘ <= ch && ch <= ‘9‘) {
30         x = x * 10 + ch - ‘0‘;
31         ch = getchar();
32     }
33     return sgn * x;
34 }
35  
36 int main() {
37     int i, j;
38     n = read();
39     for (i = 1; i <= n; ++i)
40         a[i] = read();
41     sort(a + 1, a + n + 1);
42     for (i = j = 1; i <= n; ++i) {
43         while (a[j] + eps < (lf) a[i] * 0.9)
44             ++j;
45         ans += i - j;
46     }
47     printf("%lld\n", ans);
48     return 0;
49 }