bzoj1911(Apio2010)特别行动队

题目：https://www.lydsy.com/JudgeOnline/problem.php?id=1911

斜率优化水题。别忘了斜率是递减的。

#include<iostream>
#include<cstdio>
#include<cstring>
#define ll long long
#define db double
using namespace std;
const int N=1e6+5;
int n,h,t,q[N];
ll a,b,c,s[N];
db dp[N];
db x(int k){return s[k];}
db y(int k){return a*s[k]*s[k]-b*s[k]+dp[k];}
double slope(int u,int v){return (y(v)-y(u))/(x(v)-x(u));}
int main()
{
    scanf("%d%lld%lld%lld",&n,&a,&b,&c);ll tp;
    for(int i=1;i<=n;i++)scanf("%lld",&tp),s[i]=s[i-1]+tp;
    h=1;t=1;
    for(int i=1;i<=n;i++)
    {
        while(h<t&&slope(q[h],q[h+1])>=(double)2*a*s[i])h++;
        dp[i]=y(q[h])+a*s[i]*s[i]+b*s[i]+c-2*a*s[i]*x(q[h]);
        while(h<t&&slope(q[t-1],q[t])<=slope(q[t-1],i))t--;
        q[++t]=i;
    }
    printf("%lld",(ll)dp[n]);
    return 0;
}