BZOJ 3675: [Apio2014]序列分割 动态规划 + 斜率优化 + 卡精度

Code:

#include<bits/stdc++.h>
#define N 100006
#define M 205
#define ll long long
#define setIO(s) freopen(s".in","r",stdin)
using namespace std;
int n,k,a[N],q[N];
ll s[N],f[N],g[N];
double slope(int i,int j)
{
    if(s[i]==s[j]) return -1e18;
    return 1.00*((g[i]-s[i]*s[i])-(g[j]-s[j]*s[j]))/(s[j]-s[i]);
}
int main()
{
    // setIO("input");
    int i,j;
    scanf("%d%d",&n,&k);
    for(i=1;i<=n;++i) scanf("%lld",&s[i]),s[i]+=s[i-1];
    for(j=1;j<=k;++j)
    {
        int head=1,tail=0;
        q[++tail]=0;
        for(i=1;i<=n;++i)
        {
            while(head<tail&&slope(q[head],q[head+1])<=s[i]) ++head;
            f[i]=g[q[head]]+s[q[head]]*(s[i]-s[q[head]]);
            while(head<tail&&slope(q[tail-1],q[tail])>=slope(q[tail],i)) --tail;
            q[++tail]=i;
        }
        memcpy(g,f,sizeof(g));
    }
    printf("%lld\n",f[n]);
    //     for(int x=n,i=k;i>=1;--i) x=pre[x][i], printf("%d ",x);
    return 0;
}