luogu1419 寻找段落

题目

luogu1419

代码

include

include

include

include

include

include

define N 100005

define inf 1000000000

define ll long long

using namespace std;

int n,s,t,a[N];
double sum[N];

int q[N];//q纪录起始位置
bool check(double x)
{
//将原序列全部减去平均值，sum记录前缀和
for(int i=1;i<=n;i++) sum[i]=(double)sum[i-1]+a[i]-x;
int head=1,tail=0;
for(int i=s;i<=n;i++)
{
while(tail>=head&&i-t+1>q[head]) head++;//若区间长度大于t，将起始点删去
while(tail>=head&&sum[i]-sum[i-s]>sum[i]-sum[q[tail]-1]) tail--;//若之前存在的起始点比新加入的起始点更优，删除新加入的点
q[++tail]=i-s+1;//添加起始点
if(sum[i]-sum[q[head]-1]>=0) return true;
}
return false;
}

int main()
{
scanf("%d%d%d",&n,&s,&t);
for(int i=1;i<=n;i++) scanf("%d",&a[i]);
double l=-10000,r=10000,mid,ans;//二分段落最大平均值
while(l+1e-5<r)
{
mid=(l+r)/2;
if(check(mid)) ans=mid,l=mid+1e-5;
else r=mid;
}
printf("%.3lf",ans);
return 0;
}