poj 3709 K-Anonymous Sequence 斜率优化dp

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#include<iostream>
#include<cstdio>
#include<algorithm>
using namespace std;
#define inf 0x7ffffffffffffffLL
long long a[500005];
long long sum[500005];
long long dp[500005];
int q[500005];
int n,k;

long long gdp(int i,int j)
{
    return (i-j>=k)?(dp[j]+sum[i]-sum[j]-(i-j)*a[j+1]):(inf);
}
long long gup(int j,int k)
{
    return dp[j]-dp[k]+sum[k]-sum[j]+(j)*a[j+1]-(k)*a[k+1];
}
long long gdown(int j,int k)
{
    return a[j+1]-a[k+1];
}

int main()
{
    int cas;
    scanf("%d",&cas);
    while(cas--)
    {
        scanf("%d%d",&n,&k);
        sum[0]=0;
        for(int i=1;i<=n;i++)
        {
            scanf("%lld",&a[i]);
            sum[i]=sum[i-1]+a[i];
        }
        int head=0,tail=0;
        dp[0]=q[0]=0;
        for (int i=1;i<=n;i++)
        {
            if(i-k>0)
            {
                while(head<tail&&gup(q[tail-1],q[tail])*gdown(q[tail],i-k)>=gdown(q[tail-1],q[tail])*gup(q[tail],i-k))
                    tail--;
                q[++tail]=i-k;
            }
            while(head<tail&&gup(q[head+1],q[head])<=i*gdown(q[head+1],q[head])) head++;
            dp[i]=gdp(i,q[head]);
        }
        printf("%lld\n",dp
);
    }
}