BZOJ 3156 防御准备

也是斜率优化。。。。推下式子就好了。

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#define maxn 1000050
using namespace std;
long long n,a[maxn],g[maxn],q[maxn],l,r,f[maxn];
long long read()
{
    char ch;long long data=0;
    while (ch<'0' || ch>'9') ch=getchar();
    while (ch>='0' && ch<='9')
    {
        data=data*10+ch-'0';
        ch=getchar();
    }
    return data;
}
double k(long long x,long long y)
{
    return (double)(g[x]-g[y])/(x-y);
}
void dp()
{
    f[1]=a[1];l=r=1;q[l]=1;g[1]=a[1];
    for (long long i=2;i<=n;i++)
    {
        while ((r-l) && (k(q[l],q[l+1])<=i)) l++;
        g[i]=f[i-1]+a[i]+i*(i-1)/2;
        while ((r-l) && (k(q[r-1],q[r])>k(q[r],i))) r--;
        q[++r]=i;
        f[i]=f[q[l]-1]+a[q[l]]+(i-q[l])*(i-q[l]+1)/2;
    }
}
int main()
{
    n=read();
    for (long long i=n;i>=1;i--) a[i]=read();    
    dp();
    printf("%lld\n",f[n]);
    return 0;
}