bzoj2348[Baltic 2011]Plagiarism*

 1 #include <cstdio>
 2 #include <cstring>
 3 #include <algorithm>
 4 #define inc(i,j,k) for(int i=j;i<=k;i++)
 5 #define maxn 100010
 6 using namespace std;
 7 
 8 inline int read(){
 9     char ch=getchar(); int f=1,x=0;
10     while(ch<‘0‘||ch>‘9‘){if(ch==‘-‘)f=-1; ch=getchar();}
11     while(ch>=‘0‘&&ch<=‘9‘)x=x*10+ch-‘0‘,ch=getchar();
12     return f*x;
13 }
14 int n,a[maxn],l,r; long long ans;
15 int main(){
16     n=read(); inc(i,1,n)a[i]=read(); sort(a+1,a+n+1);
17     l=1; r=1;
18     while(r<n){
19         r++; while(l<r&&a[l]+1e-8<a[r]*0.9)l++; ans+=r-l;
20     }
21     printf("%lld",ans); return 0;
22 }