[BZOJ 3437]小P的牧场：DP斜率优化

/*
User:Small
Language:C++
Problem No.:3437
*/
#include<bits/stdc++.h>
#define ll long long
#define inf 999999999
using namespace std;
const int M=1e6+5;
int n,head,tail,q[M];
ll f[M],a[M],b[M],sum[M],tot[M];
double slop(int j,int k){
return (f[k]-sum[k]+tot[k]*k-f[j]+sum[j]-tot[j]*j)/(double)(tot[k]-tot[j]);
}
ll cal(int i,int j){
return f[j]+a[i]+sum[i]-sum[j]-tot[j]*(i-j);
}
int main(){
freopen("data.in","r",stdin);//
scanf("%d",&n);
for(int i=1;i<=n;i++)
scanf("%lld",&a[i]);
for(int i=1;i<=n;i++){
scanf("%lld",&b[i]);
tot[i]=tot[i-1]+b[i];
sum[i]=sum[i-1]+tot[i-1];
}
for(int i=1;i<=n;i++){
while(head<tail&&slop(q[head],q[head+1])<i) head++;
f[i]=cal(i,q[head]);
while(head<tail&&slop(q[tail-1],q[tail])>slop(q[tail],i)) tail--;
q[++tail]=i;
}
printf("%lld",f
);
return 0;
}