【BZOJ】【P2348】【Baltic 2011】【Plagiarism】【二分】

传送门:http://www.lydsy.com/JudgeOnline/problem.php?id=2348

水题不解释

Code:

#include<bits/stdc++.h>using namespace std;const int maxn=1e5+5;int a[maxn];int n;int main(){scanf("%d",&n);for(int i=1;i<=n;i++)scanf("%d",&a[i]);sort(a+1,a+1+n);long long ans=0;for(int i=1;i<=n;i++){int l=1,r=i;while(l<r){int mid=(l+r)>>1;if(a[mid]*10>=a[i]*9)r=mid;else l=mid+1;}ans+=i-l;}cout<<ans<<endl;return 0;}