斜率优化实现初步（7） [BZOJ][4518][Sdoi2016]征途

#include<bits/stdc++.h>
using namespace std;

//#define int long long

const int MAXN=3e3+233;
int n,m,all;
int a[MAXN],sum[MAXN];
int f[MAXN][MAXN],g[MAXN][MAXN];
int head=1,tail=1,q[MAXN];

int read(){
    int x=0,f=1;char ch=getchar();
    while (!isdigit(ch)) { if (ch=='-') f=-1; ch=getchar();}
    while (isdigit(ch)) x=x*10+ch-48,ch=getchar();
    return x*f;
}

int slope(int j,int k,int opt){
    return (g[opt][j]-g[opt][k])/(sum[j]-sum[k]);
}

int pow2(int x){
    return x*x;
}

signed main(){
    n=read(),m=read();
    for (int i=1;i<=n;i++){
        a[i]=read(),sum[i]=sum[i-1]+a[i];
        f[1][i]=pow2(sum[i]),g[1][i]=f[1][i]+pow2(sum[i]);
    }
    all=sum[n];
    for (int opt=2;opt<=m;opt++){
        head=1,tail=1,q[head]=opt-1;
        for (int i=opt;i<=n;i++){
            while (head<tail&&slope(q[head+1],q[head],opt-1)<2*sum[i])
                head++;
            f[opt][i]=f[opt-1][q[head]]+pow2(sum[i]-sum[q[head]]);
            g[opt][i]=f[opt][i]+pow2(sum[i]);
            while (head<tail&&slope(i,q[tail],opt-1)<slope(q[tail],q[tail-1],opt-1))
                tail--;
            q[++tail]=i;
        }
    }
    printf("%d\n",f[m][n]*m-all*all);
    return 0;
}