bzoj5090[lydsy11月赛]组题

裸的01分数规划,二分答案,没了.

#include<cstdio>
#include<algorithm>
using namespace std;
const int maxn=100005;
int a[maxn];
double b[maxn];
double c[maxn];
typedef long long ll;
ll gcd(ll a,ll b){
  return (b==0)?a:gcd(b,a%b);
}
int main(){
  int n,k;scanf("%d%d",&n,&k);
  for(int i=1;i<=n;++i)scanf("%d",a+i);
  double l=-1e8,r=1e8;
  int R=0;
  while(r-l>1e-5){
    double mid=(l+r)/2.0;
    for(int i=1;i<=n;++i)b[i]=a[i]-mid;
    for(int i=1;i<=n;++i)b[i]+=b[i-1];
    c[0]=0;
    for(int i=1;i<=n;++i){
      c[i]=min(c[i-1],b[i]);
    }
    bool flag=false;
    for(int i=k;i<=n;++i){
      if(c[i-k]<=b[i]){
	flag=true;R=i;break;
      }
    }
    if(flag)l=mid;
    else r=mid;
  }
  double Min=0;int L=0;
  for(int j=1;j<=R-k;++j){
    if(b[j]<Min)L=j,Min=b[j];
  }
  ll sum=0;
  for(int i=L+1;i<=R;++i)sum+=a[i];
  if(sum<0){
    printf("-");sum=-sum;
  }
  ll g=gcd(sum,R-L);
  printf("%lld/%lld\n",sum/g,(R-L)/g);
  return 0;
}