bzoj3156防御准备

 1 #include <cstdio>
 2 #include <cstring>
 3 #include <algorithm>
 4 #define ll long long
 5 #define maxn 1000010
 6 #define inc(i,j,k) for(int i=j;i<=k;i++)
 7 using namespace std;
 8 
 9 int n,q[maxn],l,r; ll c[maxn],f[maxn];
10 inline int read(){
11     char ch=getchar(); int x=0,f=1;
12     while(ch<‘0‘||ch>‘9‘){if(ch==‘-‘)f=-1; ch=getchar();} while(ch>=‘0‘&&ch<=‘9‘)x=x*10+ch-‘0‘,ch=getchar();
13     return x*f;
14 }
15 double calc(int j,int k){
16     return (double)(2*f[j]-2*f[k]+j-k+(ll)j*j-(ll)k*k)/(double)(j-k);
17 }
18 int main(){
19     n=read(); inc(i,1,n)c[i]=(ll)read(); l=r=0;
20     inc(i,1,n){
21         while(l<r&&calc(q[l],q[l+1])<2*i)l++; f[i]=f[q[l]]+((ll)i-q[l])*(i-q[l]-1)/2+c[i];
22         while(l<r&&calc(q[r-1],q[r])>calc(q[r],i))r--; q[++r]=i;
23     }
24     printf("%lld",f[n]);
25 }